Changing rules_scala to custom bzlmod-compatible version and removing WORKSPACE

[sellophane]

To achieve Bazel 9+ compatiblity, we need to stop using WORKSPACE file, as --enable_workspace will be no longer available (it is already no-op in Bazel@HEAD). Regular bazelbuild/rules_scala are still not bzlmod-compatible, so we need to switch to and experimental custom ones from https://github.com/mbland/rules_scala/

Checklist

• I have filed an issue about this change and discussed potential changes with the maintainers.
• I have received the approval from the maintainers to make this change.
• This is not a stylistic, refactoring, or cleanup change.

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Discussion thread for this change

Issue number: #7232

Description of this change

[ujohnny]

looks great, have you checked it with last_green?

[sellophane]

looks great, have you checked it with last_green?

yes, it looks like it's working

[agluszak]

Why is maven_install.json removed?

[ujohnny]

Why is maven_install.json removed?

@agluszak I guess it's not, it's just repinned with -800 lines

[agluszak]

Why is maven_install.json removed?

@agluszak I guess it's not, it's just repinned with -800 lines

ahh, yes, I looked at the wrong file 🤦