test(compiler-cli): disable `emitDecoratorMetadata` in the compiler test environment (#41557)

The `emitDecoratorMetadata` compiler option does not have to be enabled
as Angular decorators are transformed by the AOT compiler. Having the
option enabled in our tests can hide issues around import preservation,
as with `emitDecoratorMetadata` enabled the TypeScript compiler itself
does not elide imports even if they are only used in type-positions.
This is unlike having `emitDecoratorMetadata` disabled, however; in that
case the Angular compiler has to actively trick TypeScript into
retaining default imports when an identifier in a type-only position has
been reified into a value position for DI purposes.

A subsequent commit addresses a bug in default import preservation
that relies on this flag being `false`.

PR Close #41557

packages/compiler-cli/test/ngtsc/env.ts

@@ -53,7 +53,7 @@ export class NgtscTestEnvironment {
 
     env.write(absoluteFrom('/tsconfig-base.json'), `{
       "compilerOptions": {
-        "emitDecoratorMetadata": true,
+        "emitDecoratorMetadata": false,
         "experimentalDecorators": true,
         "skipLibCheck": true,
         "noImplicitAny": true,

packages/compiler-cli/test/ngtsc/ngtsc_spec.ts

@@ -4648,7 +4648,7 @@ function allTests(os: string) {
 
       env.driveMain();
       const jsContents = trim(env.getContents('test.js'));
-      expect(jsContents).toContain(`import { KeyCodes } from './keycodes';`);
+      expect(jsContents).toContain(`import * as i1 from "./keycodes";`);
       expect(jsContents).toMatch(setClassMetadataRegExp('type: i1.KeyCodes'));
     });