This commit updates the docs examples to Angular v12.1.3. In addition to
updating the dependencies versions, it also updates the projects'
structure and configs to more closely match what a new v12 CLI app would
look like. See, also, the [diff][1] between a basic v11.2.11 CLI app and
a v12.1.3 one.
[1]: https://github.com/cexbrayat/angular-cli-diff/compare/11.2.11..12.1.3
PR Close#42949
Switch the JS script used for running the docs examples tests from
CommonJS to ESM format. This is necessary for upgrading the `globby`
dependency to [version 12.0.0][1] in a subsequent commit.
[1]: https://github.com/sindresorhus/globby/releases/v12.0.0
PR Close#42921
