This commit updates the docs examples to Angular v13.0.0-rc.0. In
addition to updating the dependency versions, it also updates the
projects' structure and configs to more closely match what a new v13 CLI
app would look like. See, also, the [diff][1] between a basic v12.1.3
CLI app and a v13.0.0-rc.0 one.
(NOTE: v12.1.3 was the last version for which we aligned the projects
with how a new CLI app would look like.)

Additionlly:
- Since we now use RxJS v7 in docs examples, this commit removes the
  extra CI steps to explicitly test the docs examples against RxJS v7.
- Since Angular v13 no longer supports IE, this commit removes an
  IE-specific section from `upgrade-setup.md`.

[1]: https://github.com/cexbrayat/angular-cli-diff/compare/12.1.3..13.0.0-rc.0

PR Close #43880