Those have shown to cause problems with too many concurrent downloads.
This changes kotlinc dependencies fetching to:
* use `resource/kotlinc-dependencies` if available (which is the case
for the internal repo)
* otherwise, download them from maven.
This means sha256 hashes need to be written down for bazel.
By adding `java/kotlinc-extractor/deps/dev` to `PATH`, one gets a
`kotlinc` wrapper that takes care of downloading and extracting the
desired version of `kotlinc` on demand. The desired version can be
selected with `kotlinc --select x.y.z`, or left to the current default
of `1.9.0`.
Moreover, this default version is integrated with the Bazel build, so
that when using this wrapper, changes in the selected version will be
picked up to define the default single version kotlin extractor build,
without needing to do anything else (like `bazel fetch --force` or
similar).
Selected and installed version data is stored in `.gitignore`d files
in the same directory, and can be cleared with `kotlinc --clear`.
