Provide a unified (lsp-interface INTERFACE ...) pcase form

This commit provides a new unified pcase form (lsp-interface INTERFACE ...) to
replace the old per-interface (INTERFACE ...) forms -- the latter are now
deprecated. (Unfortunately, I don't think there's a way to mark a pcase form as
obsolete.)

I've turned the existing pcase-defmacro definition into a helper function. The
new pcase form delegates to that helper function, and the old pcase forms now
delegate to the new form.

This change addresses a few issues, which are detailed in #4430. In short:

* The existing forms aren't namespaced.
* The lsp-mode package adds hundreds of forms, which each add several lines to
pcase's generated docstring, adding up to over 1000 lines.
* Starting in Emacs 1.31, the number of forms added by lsp-mode causes a
noticeable slowdown when loading the interactive help for pcase.

lsp-protocol.el

@@ -129,7 +129,7 @@ Allowed params: %s" interface (reverse (-map #'cl-first params)))
                                               $$result))
                                    (-partition 2 plist))
                              $$result)))
-                    `(pcase-defmacro ,interface (&rest property-bindings)
+                    `(cl-defun ,(intern (format "lsp--pcase-macroexpander-%s" interface)) (&rest property-bindings)
                        ,(if lsp-use-plists
                             ``(and
                                (pred listp)
@@ -225,6 +225,8 @@ Allowed params: %s" interface (reverse (-map #'cl-first params)))
                                              output-bindings)
                                        (setf current-list (cddr current-list))))))
                                  output-bindings))))
+                    `(pcase-defmacro ,interface (&rest property-bindings)
+                       ``(lsp-interface ,',interface ,@property-bindings))
                     (-mapcat (-lambda ((label . name))
                                (list
                                 `(defun ,(intern (format "lsp:%s-%s"
@@ -246,6 +248,21 @@ Allowed params: %s" interface (reverse (-map #'cl-first params)))
          (apply #'append)
          (cl-list* 'progn))))
 
+(pcase-defmacro lsp-interface (interface &rest property-bindings)
+  "If EXPVAL is an instance of the LSP interface INTERFACE, destructure its
+properties.
+
+Each :PROPERTY key may be followed by an optional PATTERN, which is a `pcase'
+pattern to apply to the property value. Otherwise, PROPERTY is bound to the
+property value.
+
+\(fn INTERFACE [:PROPERTY [PATTERN]]...)"
+  (cl-check-type interface symbol)
+  (let ((lsp-pcase-macroexpander
+         (intern (format "lsp--pcase-macroexpander-%s" interface))))
+    (cl-assert (fboundp lsp-pcase-macroexpander) "not a known LSP interface: %s" interface)
+    (apply lsp-pcase-macroexpander property-bindings)))
+
 (if lsp-use-plists
     (progn
       (defun lsp-get (from key)