fix(compiler): various squashed fixes for the new ngc

introduce the option `allowEmptyCodegenFiles` to generate all generated files,
even if they are empty.
- also provides the original source files from which the file was generated
  in the write file callback
- needed e.g. for G3 when copying over pinto mod names from the original component
  to all generated files

use `importAs` from flat modules when writing summaries
- i.e. prevents incorrect entries like @angular/common/common in the .ngsummary.json files.

change interaction between ng and ts to prevent race conditions
- before Angular would rely on TS to first read the file for which we generate files,
  and then the generated files. However, this can break easily when we reuse an old program.

don’t generate files for sources that are outside of `rootDir`
(see #19337)

packages/bazel/src/ng_module.bzl

@@ -67,6 +67,7 @@ def _ngc_tsconfig(ctx, files, srcs, **kwargs):
   return dict(tsc_wrapped_tsconfig(ctx, files, srcs, **kwargs), **{
       "angularCompilerOptions": {
           "generateCodeForLibraries": False,
+          "allowEmptyCodegenFiles": True,
           # FIXME: wrong place to de-dupe
           "expectedOut": depset([o.path for o in expected_outs]).to_list()
       }

packages/bazel/src/ngc-wrapped/index.ts

@@ -40,24 +40,21 @@ function runOneBuild(args: string[], inputs?: {[path: string]: string}): boolean
   if (args[0] === '-p') args.shift();
   // Strip leading at-signs, used to indicate a params file
   const project = args[0].replace(/^@+/, '');
-  let fileLoader: FileLoader;
-  if (inputs) {
-    fileLoader = new CachedFileLoader(fileCache, ALLOW_NON_HERMETIC_READS);
-    // Resolve the inputs to absolute paths to match TypeScript internals
-    const resolvedInputs: {[path: string]: string} = {};
-    for (const key of Object.keys(inputs)) {
-      resolvedInputs[path.resolve(key)] = inputs[key];
-    }
-    fileCache.updateCache(resolvedInputs);
-  } else {
-    fileLoader = new UncachedFileLoader();
-  }
   const [{options: tsOptions, bazelOpts, files, config}] = parseTsconfig(project);
   const expectedOuts = config['angularCompilerOptions']['expectedOut'];
 
   const {basePath} = ng.calcProjectFileAndBasePath(project);
   const compilerOpts = ng.createNgCompilerOptions(basePath, config, tsOptions);
-  const {diagnostics} = compile({fileLoader, compilerOpts, bazelOpts, files, expectedOuts});
+  const tsHost = ts.createCompilerHost(compilerOpts, true);
+  const {diagnostics} = compile({
+    allowNonHermeticReads: ALLOW_NON_HERMETIC_READS,
+    compilerOpts,
+    tsHost,
+    bazelOpts,
+    files,
+    inputs,
+    expectedOuts
+  });
   return diagnostics.every(d => d.category !== ts.DiagnosticCategory.Error);
 }
 
@@ -71,14 +68,28 @@ export function relativeToRootDirs(filePath: string, rootDirs: string[]): string
   return filePath;
 }
 
-export function compile(
-    {fileLoader, compilerOpts, bazelOpts, files, expectedOuts, gatherDiagnostics}: {
-      fileLoader: FileLoader,
-      compilerOpts: ng.CompilerOptions,
-      bazelOpts: BazelOptions,
-      files: string[],
-      expectedOuts: string[], gatherDiagnostics?: (program: ng.Program) => ng.Diagnostics
-    }): {diagnostics: ng.Diagnostics, program: ng.Program} {
+export function compile({allowNonHermeticReads, compilerOpts, tsHost, bazelOpts, files, inputs,
+                         expectedOuts, gatherDiagnostics}: {
+  allowNonHermeticReads: boolean,
+  compilerOpts: ng.CompilerOptions,
+  tsHost: ts.CompilerHost, inputs?: {[path: string]: string},
+  bazelOpts: BazelOptions,
+  files: string[],
+  expectedOuts: string[], gatherDiagnostics?: (program: ng.Program) => ng.Diagnostics
+}): {diagnostics: ng.Diagnostics, program: ng.Program} {
+  let fileLoader: FileLoader;
+  if (inputs) {
+    fileLoader = new CachedFileLoader(fileCache, ALLOW_NON_HERMETIC_READS);
+    // Resolve the inputs to absolute paths to match TypeScript internals
+    const resolvedInputs: {[path: string]: string} = {};
+    for (const key of Object.keys(inputs)) {
+      resolvedInputs[path.resolve(key)] = inputs[key];
+    }
+    fileCache.updateCache(resolvedInputs);
+  } else {
+    fileLoader = new UncachedFileLoader();
+  }
+
   if (!bazelOpts.es5Mode) {
     compilerOpts.annotateForClosureCompiler = true;
     compilerOpts.annotationsAs = 'static fields';
@@ -89,7 +100,6 @@ export function compile(
   }
 
   const writtenExpectedOuts = [...expectedOuts];
-  const tsHost = ts.createCompilerHost(compilerOpts, true);
 
   const originalWriteFile = tsHost.writeFile.bind(tsHost);
   tsHost.writeFile =