refactor(compiler): add ability to produce stub .ngfactory / .ngsummary files (#16963)

These files are needed so that:
- user code can compile even without real codegen
- as tsc transformers cannot create but only change existing files
  in the transformation pipeline.

packages/compiler-cli/src/codegen.ts

@@ -38,8 +38,9 @@ export class CodeGenerator {
 
   codegen(): Promise<any> {
     return this.compiler
-        .compileAllAsync(this.program.getSourceFiles().map(
+        .analyzeModulesAsync(this.program.getSourceFiles().map(
             sf => this.ngCompilerHost.getCanonicalFileName(sf.fileName)))
+        .then(analyzedModules => this.compiler.emitAllImpls(analyzedModules))
         .then(generatedModules => {
           generatedModules.forEach(generatedModule => {
             const sourceFile = this.program.getSourceFile(generatedModule.srcFileUrl);