fix(@jsii/spec): speed up assembly validation by 20x for large libraries

packages/@jsii/spec/package.json

@@ -31,7 +31,7 @@
     "package": "package-js"
   },
   "dependencies": {
-    "jsonschema": "^1.4.1"
+    "ajv": "^8.11.0"
   },
   "devDependencies": {
     "jsii-build-tools": "^0.0.0",

packages/@jsii/spec/src/validate-assembly.ts

@@ -1,16 +1,22 @@
-import { Schema, Validator } from 'jsonschema';
+import Ajv from 'ajv';
 
 import { Assembly } from './assembly';
 
 // eslint-disable-next-line @typescript-eslint/no-require-imports, @typescript-eslint/no-var-requires
-export const schema: Schema = require('../schema/jsii-spec.schema.json');
+export const schema = require('../schema/jsii-spec.schema.json');
 
 export function validateAssembly(obj: any): Assembly {
-  const validator = new Validator();
-  validator.addSchema(schema); // For definitions
-  const result = validator.validate(obj, schema, { nestedErrors: true });
-  if (result.valid) {
-    return obj;
+  const ajv = new Ajv();
+  const validate = ajv.compile(schema);
+  validate(obj);
+
+  if (validate.errors) {
+    throw new Error(
+      `Invalid assembly:\n${validate.errors
+        .map((e) => ` * ${e.message}`)
+        .join('\n')
+        .toString()}`,
+    );
   }
-  throw new Error(`Invalid assembly:\n${result.toString()}`);
+  return obj;
 }