Upgrade to sbt 1.5.0

[gabro]

Summary of the main changes (I've split them by commit to ease the review):

• Remove sbt-dotty in favor of native support (it requires replacing withDottyCompat)
• Remove workaround for an sbt bug around semanticdb scalac options
• Remove deprecated sbt syntax in favor of the new unified slash syntax
• Switch from csbt to sbt on Windows CI (to fix a classloading issue)
• Remove MUnitReporterPluin from our docs (sort of a followup of Remove documentation on how to setup test reports. #305), since it was blocking the CI due to invalid credentials
• Update the getting started docs to add MUnit as a custom sbt test framework only on < 1.5.0

[SethTisue]

🙀

[error] com.google.cloud.storage.StorageException: The project to be billed is associated with a closed billing account.
[error] 	at com.google.cloud.storage.spi.v1.HttpStorageRpc.translate(HttpStorageRpc.java:233)

[gabro]

@SethTisue Yeah, that's a known issue I've been avoiding to deal with. The account was @olafurpg's personal account and it expired IIRC. I will disable it for the time being.

[gabro]

✅ 🎉

[olafurpg]

LGTM 👍 Thank you!

@SethTisue I think it's a cool idea to collect historical test reports but the MUnit implementation wasn't fully fleshed out. For example, there was no good way to properly query/filter the data if you only want a report for the last month or something like that.