refactor(@ngtools/webpack): use Angular compiler CLI private tooling export

The `@angular/compiler-cli/private/tooling` package export is now used instead
of the main package export to allow cleanup of the compiler-cli package. This
secondary export has existed for several major versions.

Author: clydin

packages/ngtools/webpack/src/ivy/plugin.ts

@@ -74,6 +74,7 @@ interface FileEmitHistoryItem {
 export class AngularWebpackPlugin {
   private readonly pluginOptions: AngularWebpackPluginOptions;
   private compilerCliModule?: typeof import('@angular/compiler-cli');
+  private compilerCliToolingModule?: typeof import('@angular/compiler-cli/private/tooling');
   private watchMode?: boolean;
   private ngtscNextProgram?: NgtscProgram;
   private builder?: ts.EmitAndSemanticDiagnosticsBuilderProgram;
@@ -107,6 +108,18 @@ export class AngularWebpackPlugin {
     return this.compilerCliModule;
   }
 
+  private get compilerCliTooling(): typeof import('@angular/compiler-cli/private/tooling') {
+    // The compilerCliToolingModule field is guaranteed to be defined during a compilation
+    // due to the `beforeCompile` hook. Usage of this property accessor prior to the
+    // hook execution is an implementation error.
+    assert.ok(
+      this.compilerCliToolingModule,
+      `'@angular/compiler-cli' used prior to Webpack compilation.`,
+    );
+
+    return this.compilerCliToolingModule;
+  }
+
   get options(): AngularWebpackPluginOptions {
     return this.pluginOptions;
   }
@@ -688,18 +701,17 @@ export class AngularWebpackPlugin {
   }
 
   private async initializeCompilerCli(): Promise<void> {
-    if (this.compilerCliModule) {
-      return;
-    }
-
     // This uses a dynamic import to load `@angular/compiler-cli` which may be ESM.
     // CommonJS code can load ESM code via a dynamic import. Unfortunately, TypeScript
     // will currently, unconditionally downlevel dynamic import into a require call.
     // require calls cannot load ESM code and will result in a runtime error. To workaround
     // this, a Function constructor is used to prevent TypeScript from changing the dynamic import.
     // Once TypeScript provides support for keeping the dynamic import this workaround can
     // be dropped.
-    this.compilerCliModule = await new Function(`return import('@angular/compiler-cli');`)();
+    this.compilerCliModule ??= await new Function(`return import('@angular/compiler-cli');`)();
+    this.compilerCliToolingModule ??= await new Function(
+      `return import('@angular/compiler-cli/private/tooling');`,
+    )();
   }
 
   private async addFileEmitHistory(

packages/ngtools/webpack/src/ivy/transformation.ts

@@ -47,7 +47,7 @@ export function createAotTransformers(
 
 export function createJitTransformers(
   builder: ts.BuilderProgram,
-  compilerCli: typeof import('@angular/compiler-cli'),
+  compilerCli: typeof import('@angular/compiler-cli/private/tooling'),
   options: {
     inlineStyleFileExtension?: string;
   },