Move to the official bazel worker api (with workspace support)

[agluszak]

Continuation of https://github.com/bazelbuild/rules_kotlin/pull/1218

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[Bencodes]

For context behind why I never merged the worker API changes - The worker impl. that Google released only supports Bzlmod and does not support workspace files, so we'd have to maintain that scaffolding ourselves until we decide to fully cut WORKSPACE support (we can have that discussion).

Didn't seem worth it to make local development and external developer overrides more complicated for our remaining WORKSPACE users with not much actual benefit.