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
Previously, there were no tests for the `universal` docs example. This
meant that the project was not tested at all (not even ensuring that it
can be built successfully).
This commit adds e2e tests for the `universal` example (ported from
`toh-pt6` and cleaned up) and also verifies that the project can be
built successfully (including the server).
PR Close#36483
