fix(compiler): compile .ngfactory.ts files even if nobody references them. (#16899)

This is especially important for library authors, as they will
not reference the .ngfactory.ts files.

Fixes #16741

packages/compiler-cli/src/codegen.ts

@@ -36,18 +36,19 @@ export class CodeGenerator {
       public host: ts.CompilerHost, private compiler: compiler.AotCompiler,
       private ngCompilerHost: CompilerHost) {}
 
-  codegen(): Promise<any> {
+  codegen(): Promise<string[]> {
     return this.compiler
         .analyzeModulesAsync(this.program.getSourceFiles().map(
             sf => this.ngCompilerHost.getCanonicalFileName(sf.fileName)))
         .then(analyzedModules => this.compiler.emitAllImpls(analyzedModules))
         .then(generatedModules => {
-          generatedModules.forEach(generatedModule => {
+          return generatedModules.map(generatedModule => {
             const sourceFile = this.program.getSourceFile(generatedModule.srcFileUrl);
             const emitPath = this.ngCompilerHost.calculateEmitPath(generatedModule.genFileUrl);
             const source =
                 generatedModule.source || compiler.toTypeScript(generatedModule, PREAMBLE);
             this.host.writeFile(emitPath, source, false, () => {}, [sourceFile]);
+            return emitPath;
           });
         });
   }