Update build to handle documentation issues being errors

Previously, documentation issues had `lint` severity (which was between
`warning` and `hide`) by default. However, a recent change in Metalava
switched documentation issues to `error`. That broke some `droidstubs`
modules that either did not specify `api_lint` or were previously allow
listed to not use `--lints-as-errors`.

This change adds `--error-when-new-category Documentation` to the
Metalava arguments on any use of `droidstubs` that did not previously
specify `--lints-as-errors` to prevent the build breakage while still
warning developers of the problem and preventing new cases being added.

Bug: 343157584
Test: ./gradlew
Change-Id: Id80bc05e2dade580b2f3ac6416aeeed6b64ba22a