go_sdk: store SDK filenames and hashes in lockfile facts (#4393)

**What type of PR is this?**

Feature

**What does this PR do? Why is it needed?**

This moves the download of the "all versions" JSON, which can't hit the
repository cache, from each individual `go_download_sdk` into the module
extension. If the current version of Bazel supports facts, this
information will also be persisted in the lockfile, allowing for truly
airgapped builds assuming an up-to-date download (formerly repository)
cache.

See https://github.com/bazelbuild/bazel/pull/26198 for the PR that adds
facts support to Bazel.

**Which issues(s) does this PR fix?**

Fixes #3945 

**Other notes for review**