Add current api check as validation for from-text stub generation

Currently, there is no build action ensuring that the API text files are
up to date, unless a user runs `m checkapi` or `m update-api`. This
means that the user must run `m update-api` after making a change that
modifies api surface(s), so that the API text file reflects the local
change. This adds additional layer of action to developers, and it is
not guaranteed that the developer will always run `m update-api` after
making an api surface-affecting changes.

To prevent such mistake, this change adds droidstub-level api check as
validation for from-text stub generation. With this change, the build
will fail if the API text file is not up to date and the user must run
`m update-api` when making api surface-affecting local changes.

The validation is done by adding all droidstubs modules associated with
the java_api_contributions passed to java_api_library via
`api_contributions` as dependency and setting the current api timestamp
files as the validations for the from-text stubs generating build rule.

The full api surface libraries will not run the validations to avoid
circular dependency. However, all java_sdk_library generated
java_api_library modules will run validations, mapped to the droidstubs
in the same api domaion.

If the user sets the environment variable `DISABLE_STUB_VALIDATION=true`, validation
actions are not run. Validation actions run by default.

Test: m nothing --build-from-text-stub and run ninja query to verify `check_current_api.timestamp`s are listed as validation \
      DISABLE_STUB_VALIDATION=true m nothing --build-from-text-stub and run ninja query to verify that validation actions are not added
Bug: 288624417
Change-Id: I329e6438fe8f3ac30d8c6a971d57853ed6b0d150