perf(compiler): speed up watch mode (#19275)

- don’t regenerate code for .d.ts files when
  an oldProgram is passed to `createProgram`
- cache `fileExists` / `getSourceFile` / `readFile` in watch mode
- refactor tests to share common code in `test_support`
- support `—diagnostic` command line to print total time
  used per watch mode compilation.
PR Close #19275

packages/compiler-cli/test/transformers/compiler_host_spec.ts

@@ -39,7 +39,7 @@ describe('NgCompilerHost', () => {
     ngHost = createNgHost({files}),
   }: {files?: Directory, options?: CompilerOptions, ngHost?: CompilerHost} = {}) {
     return new TsCompilerAotCompilerTypeCheckHostAdapter(
-        ['/tmp/index.ts'], options, ngHost, new MetadataCollector(), codeGenerator);
+        ['/tmp/index.ts'], options, ngHost, new MetadataCollector(), codeGenerator, new Map());
   }
 
   describe('fileNameToModuleName', () => {