fix(docs-infra): correctly add `polyfills.ts` file as boilerplate for `i18n` docs examples (#38173)

Docs examples of type `i18n` need a slightly modified version of
`polyfills.ts` that imports `@angular/localize/init`. Previously, this
file was not included in `i18n` example projects for two reasons:

- While the file was included in the `i18n` boilerplate files (at
  `aio/tools/examples/shared/boilerplate/i18n/`), it was not included in
  the boilerplate file list in `example-boilerplate.js`.
- The file was in the wrong location: It was located at the project root
  instead of inside the `src/` directory.

This commit addresses the above issues (i.e. adds the file to the
boilerplate file list for `i18n` projects and moves the file inside the
`src/` directory).

PR Close #38173

aio/tools/examples/example-boilerplate.js

@@ -32,7 +32,7 @@ const cliRelativePath = BOILERPLATE_PATHS.cli.map(file => `../cli/${file}`);
 
 BOILERPLATE_PATHS.elements = [...cliRelativePath, 'package.json', 'src/polyfills.ts'];
 
-BOILERPLATE_PATHS.i18n = [...cliRelativePath, 'angular.json', 'package.json'];
+BOILERPLATE_PATHS.i18n = [...cliRelativePath, 'angular.json', 'package.json', 'src/polyfills.ts'];
 
 BOILERPLATE_PATHS['service-worker'] = [...cliRelativePath, 'angular.json', 'package.json'];
 

aio/tools/examples/example-boilerplate.spec.js

@@ -11,7 +11,7 @@ describe('example-boilerplate tool', () => {
     const sharedNodeModulesDir = path.resolve(sharedDir, 'node_modules');
     const BPFiles = {
       cli: 20,
-      i18n: 2,
+      i18n: 3,
       universal: 2,
       systemjs: 7,
       common: 1,