Make scalafmt version dynamic in ScalafmtModule

[pieter-bos]

I see that the scalafmt version has been stuck at 3.7.15 for a bit, since java 8 support was dropped past that version. I'd like to use some bugfixes from later versions, so how about we make the version dynamic in ScalafmtModule? Scalafmt offers a nice binary-compatible interface through scalafmt-interfaces, so mill itself can stick with that. Some considerations:

• The BuildInfo entry does not make much sense now, since in general the interfaces version is unrelated to any used scalafmt version.
• I'm not a fan of setting an arbitrary old default version for scalafmtVersion, but I guess this is required for compatibility (?)

Thanks!

[lefou]

I'd like to use some bugfixes from later versions, so how about we make the version dynamic in ScalafmtModule?

scalafmt-dynamic-3.7.15 is dynamically using the scalafmt version specified in .scalafmt.conf. So you should be able to use whatever newer version you want. That's the point of using scalafmt-dynamic with a config file over a configuration inside build.sc.

[pieter-bos]

I see! I tried this earlier and it had no effect then, but it's working now, so I must have missed something. Sorry for the PR noise!

[lefou]

No problem and thanks for your contribution!

If you find that our documentation could be improved, feel free to open another PR!