[roll] Roll fuchsia [fx][bazel] Ensure proper Ninja build plan regeneration.

`fx bazel` first check whether the Ninja build plan needs
to be regenerated before rebuilding the workspace.

The regeneration itself was performed directly in update_workspace.py
by invoking Ninja, but didn't define environment variables in the
same way as `fx build`, resulting problems, such as broken RBE-enabled
builds when invoking `fx bazel` just after modifying a `BUILD.gn`
file.

This CL fixes the issue by doing the following:

- Moving the fast 'build plan freshness' check to its own
  Python script, invoked from `fx bazel`.

- Ensure that `fx build` is called to regenerate the build plan
  if needed, to ensure consistent environment variables in
  all cases.

+ Ensure `fx-rbe-enabled` is not called twice by `fx build`
  when `--fint-params` is not used (the function is already
  called by `fx-run-ninja` defined lib `lib/vars.sh`.

Manual testing:

  1) Ensure your have RBE enabled in your args.gn

  2) `touch BUILD.gn`, to force a Ninja regen on the next invocation.

  3) `fx bazel`, which will launch the regen operation before
     invoking Ninja.

Before this CL, step 3) would print many Ninja errors such as:
```
../../build/rbe/reclient_cxx.sh: line 112: RBE_server_adress: unbound variable
```

This does not happen after the CL, because the environment variable
is correctly defined when invoking Ninja.

Original-Bug: b/315393497
Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/957556
Original-Revision: 8cf98c6678802b960c45dd607e4869d3f7740e93
GitOrigin-RevId: 9a953d2724adddc3b2bf3655cb8ed480a8815ab8
Change-Id: Icb177d5ec7b6d1be40cb03a666699d20ec2efe9d