Provide base schema classes for following rman plugins

    - DisplayFilter
    - SampleFilter (example PxrMurkFilter)
    - Integrator
    - Projection

    These typed schema classes provide default connectableAPIBehavior.

    Re-ran usdGenSchema on this to update generatedSchema.usda and
    plugInfo.json

In subsequent change, these base classes will be used to derive auto generated schemas from args files.
And in another subsequent change, these will be documented to be used as terminal connections in appropriate API schema (PxrRenderTerminalsAPI)

(Internal change: 2199277)

third_party/renderman-24/plugin/usdRiPxr/generatedSchema.usda

@@ -3,6 +3,38 @@
     "WARNING: THIS FILE IS GENERATED BY usdGenSchema.  DO NOT EDIT."
 )
 
+class "PxrProjectionPluginBase" (
+    doc = """Base Schema class which other PxrProjection plugins will inherit.
+    It also provides UsdShade connectability for all classes that derive from
+    it."""
+)
+{
+}
+
+class "PxrSampleFilterPluginBase" (
+    doc = """Base Schema class which other PxrSampleFiler plugins will inherit. 
+    It also provides UsdShade connectability for all classes that derive from
+    it."""
+)
+{
+}
+
+class "PxrDisplayFilterPluginBase" (
+    doc = """Base Schema class which other PxrDisplayFiler plugins will inherit.
+    It also provides UsdShade connectability for all classes that derive from
+    it."""
+)
+{
+}
+
+class "PxrIntegratorPluginBase" (
+    doc = """Base Schema class which other PxrIntegrator plugins will inherit.
+    It also provides UsdShade connectability for all classes that derive from
+    it."""
+)
+{
+}
+
 class "PxrCameraProjectionAPI" (
     doc = """API schema that is auto-applied _only_ to UsdGeomCamera and 
     provides a RenderMan-specific projection output terminal to UsdGeomCamera

third_party/renderman-24/plugin/usdRiPxr/plugInfo.json

@@ -101,6 +101,17 @@
                         ], 
                         "schemaKind": "singleApplyAPI"
                     }, 
+                    "UsdRiPxrDisplayFilterPluginBase": {
+                        "alias": {
+                            "UsdSchemaBase": "PxrDisplayFilterPluginBase"
+                        }, 
+                        "autoGenerated": true, 
+                        "bases": [
+                            "UsdTyped"
+                        ], 
+                        "providesUsdShadeConnectableAPIBehavior": true, 
+                        "schemaKind": "abstractTyped"
+                    }, 
                     "UsdRiPxrDistantLightAPI": {
                         "alias": {
                             "UsdSchemaBase": "PxrDistantLightAPI"
@@ -157,6 +168,17 @@
                         ], 
                         "schemaKind": "concreteTyped"
                     }, 
+                    "UsdRiPxrIntegratorPluginBase": {
+                        "alias": {
+                            "UsdSchemaBase": "PxrIntegratorPluginBase"
+                        }, 
+                        "autoGenerated": true, 
+                        "bases": [
+                            "UsdTyped"
+                        ], 
+                        "providesUsdShadeConnectableAPIBehavior": true, 
+                        "schemaKind": "abstractTyped"
+                    }, 
                     "UsdRiPxrMeshLightAPI": {
                         "alias": {
                             "UsdSchemaBase": "PxrMeshLightAPI"
@@ -184,6 +206,17 @@
                         ], 
                         "schemaKind": "singleApplyAPI"
                     }, 
+                    "UsdRiPxrProjectionPluginBase": {
+                        "alias": {
+                            "UsdSchemaBase": "PxrProjectionPluginBase"
+                        }, 
+                        "autoGenerated": true, 
+                        "bases": [
+                            "UsdTyped"
+                        ], 
+                        "providesUsdShadeConnectableAPIBehavior": true, 
+                        "schemaKind": "abstractTyped"
+                    }, 
                     "UsdRiPxrRampLightFilter": {
                         "alias": {
                             "UsdSchemaBase": "PxrRampLightFilter"
@@ -217,6 +250,17 @@
                         ], 
                         "schemaKind": "concreteTyped"
                     }, 
+                    "UsdRiPxrSampleFilterPluginBase": {
+                        "alias": {
+                            "UsdSchemaBase": "PxrSampleFilterPluginBase"
+                        }, 
+                        "autoGenerated": true, 
+                        "bases": [
+                            "UsdTyped"
+                        ], 
+                        "providesUsdShadeConnectableAPIBehavior": true, 
+                        "schemaKind": "abstractTyped"
+                    }, 
                     "UsdRiPxrSphereLightAPI": {
                         "alias": {
                             "UsdSchemaBase": "PxrSphereLightAPI"

third_party/renderman-24/plugin/usdRiPxr/schema.usda

@@ -16,6 +16,66 @@ over "GLOBAL" (
 {
 }
 
+class "PxrProjectionPluginBase" (
+    inherits = </Typed>
+    customData = {
+        string className = "ProjectionPluginBase"
+        dictionary extraPlugInfo = {
+            bool providesUsdShadeConnectableAPIBehavior = 1
+        }
+    }
+    doc = """Base Schema class which other PxrProjection plugins will inherit.
+    It also provides UsdShade connectability for all classes that derive from
+    it."""
+)
+{
+}
+
+class "PxrSampleFilterPluginBase" (
+    inherits = </Typed>
+    customData = {
+        string className = "SampleFilterPluginBase"
+        dictionary extraPlugInfo = {
+            bool providesUsdShadeConnectableAPIBehavior = 1
+        }
+    }
+    doc = """Base Schema class which other PxrSampleFiler plugins will inherit. 
+    It also provides UsdShade connectability for all classes that derive from
+    it."""
+)
+{
+}
+
+class "PxrDisplayFilterPluginBase" (
+    inherits = </Typed>
+    customData = {
+        string className = "DisplayFilterPluginBase"
+        dictionary extraPlugInfo = {
+            bool providesUsdShadeConnectableAPIBehavior = 1
+        }
+    }
+    doc = """Base Schema class which other PxrDisplayFiler plugins will inherit.
+    It also provides UsdShade connectability for all classes that derive from
+    it."""
+)
+{
+}
+
+class "PxrIntegratorPluginBase" (
+    inherits = </Typed>
+    customData = {
+        string className = "IntegratorPluginBase"
+        dictionary extraPlugInfo = {
+            bool providesUsdShadeConnectableAPIBehavior = 1
+        }
+    }
+    doc = """Base Schema class which other PxrIntegrator plugins will inherit.
+    It also provides UsdShade connectability for all classes that derive from
+    it."""
+)
+{
+}
+
 class "PxrCameraProjectionAPI" (
     customData = {
         token[] apiSchemaAutoApplyTo = ["Camera"]