Add bundlebun to JS Runtimes and Tools

[yaroslav]

Before submitting your pull request:

• If you're referencing a gem by its GitHub repository (e.g. rails/rails), please verify
  that it is not packaged as a Ruby gem. (If it is packaged as a gem, please reference it
  by its gem name instead, e.g. rails.)
• Make sure the CI build passes, we validate your proposed changes in the test suite :)

Adds bundlebun, a vendored Bun runtime, to Runtimes and Tools (as a builder)