Misc improvements in compiler options handling

[Gedochao]

This is largely a (much belated) follow-up to scala/scala3#19766, which revamped how compiler settings can be called. We haven't been supporting some of the new syntax.
The actual follow-up we plan for is #2867, this PR should be treated as the first step.

Changes include

• compiler options can now be passed with - or -- prefixes interchangably (-Wunused:locals means exactly the same as --Wunused:locals)
• compiler option values can be passed with : or a space, interchangably (-Wunused:locals means the same as -Wunused locals)
  • this applies to repeatable options, so now -Wunused:locals,privates, -Wunused:locals -Wunusedprivates and -Wunused locals -Wunused privates are all synonyms.
• some options which previously required to be passed via -O now don't:
  • -explain
  • -experimental
• some options which should have allowed to be repeatable (as they accept a list of values) now actually do
  • -Wunused
  • -coverage-exclude-classlikes
  • -coverage-exclude-files
  • -Wshadow
  • -Xlint
  • -Xmacro-settings
  • -Xplugin-disable
  • -Xplugin-require
  • -Yimports
  • -Yfrom-tasty-ignore-list
• --source (which used to indicate a source jar artifact is to be produced by the package sub-command) and -source (a compiler option) are now synonyms, as treated by the Scala compiler
  • to produce a source jar, use --src or --sources instead.
• the changes have been covered with tests where applicable (within reason, we can't test for each compiler option)
  • these tests are also good preparation for the rewrite necessary for Improve Scala compiler settings integration #2867

[Gedochao]

Note: the changes are rather large, although I tried to split the commits in a way so that it's easy to review. Let me know if I should split it into smaller bits.

[tgodzik]

Looks good!