Fallback to UTF-8 in setup-ide

[JD557]

Uses UTF-8 as the default charset in setup-ide as that seems to be the format expected by the other tools (such as metals).

Closes #2598

[JD557]

I'm not really sure why the CI is failing. I see:

Thu, 30 Nov 2023 21:43:09 GMT ==> X sclicheck.DocTests.command basics  32.382s sclicheck.FailedCheck: [website/docs/commands/basics.md:320] Commands failed.
Thu, 30 Nov 2023 21:43:09 GMT     at sclicheck.FailedCheck$.apply(sclicheck.scala:64)
Thu, 30 Nov 2023 21:43:09 GMT     at sclicheck.sclicheck$package$.check(sclicheck.scala:68)
Thu, 30 Nov 2023 21:43:09 GMT     at sclicheck.sclicheck$package$.runCommand$1(sclicheck.scala:251)
Thu, 30 Nov 2023 21:43:09 GMT     at sclicheck.sclicheck$package$.checkFile$$anonfun$1(sclicheck.scala:310)
Thu, 30 Nov 2023 21:43:09 GMT     at scala.collection.immutable.Vector.foreach(Vector.scala:1895)
Thu, 30 Nov 2023 21:43:09 GMT     at sclicheck.sclicheck$package$.checkFile(sclicheck.scala:317)
Thu, 30 Nov 2023 21:43:09 GMT     at sclicheck.DocTests.$init$$$anonfun$3$$anonfun$1$$anonfun$1(DocTests.scala:36)

I assumed this meant that I need to run ./mill -i generate-reference-doc.run, but that doesn't seem to change anything...

[JD557]

Oh, looks like it might have been a flaky test, thanks for re-triggering the build. :)

[Gedochao]

LGTM
Some context: we use UTF-8 everywhere, so this makes sense.
We should make it customisable at some point, the relevant ticket to track is #1390