cross-build to sbt 2.x

[bjaglin]

https://www.scala-sbt.org/2.x/docs/en/changes/migrating-from-sbt-1.x.html
https://github.com/sbt/sbt/wiki/sbt-2.x-plugin-migration

WIP - I'll iterate on that PR in the coming days to find the actual blockers

• [2.x] Missing implementation of Def.inputTaskDyn sbt/sbt#7707

  [error] -- [E008] Not Found Error: /home/brice/git/scala/sbt-scalafix/src/main/scala/scalafix/sbt/ScalafixPlugin.scala:380:34 
  [error] 380 |    InputTask.createDyn(InputTask.initParserAsInput(scalafixParser))(
  [error]     |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  [error]     |       value initParserAsInput is not a member of object sbt.InputTask

• [error] -- [E189] Not Found Error: /home/brice/git/scala/sbt-scalafix/src/main/scala/scalafix/sbt/ScalafixPlugin.scala:246:13 
  [error] 246 |        case Value(v: UpdateReport) => v
  [error]     |             ^^^^^
  [error]     |             no pattern match extractor named Value was found
  [error]     |
  [error]     | longer explanation available when compiling with `-explain`

• [error] -- [E172] Type Error: /home/brice/git/scala/sbt-scalafix/src/main/scala/scalafix/sbt/ScalafixPlugin.scala:603:45 
  [error] 603 |                write(stampFile(path.toFile))
  [error]     |                                             ^
  [error]     |Ambiguous given instances: both object StringJsonFormat in trait PrimitiveFormats and value argFormat match type sjsonnew.JsonWriter[String] of a context parameter of method write

• [error] -- [E008] Not Found Error: /home/brice/git/scala/sbt-scalafix/src/main/scala/scalafix/sbt/ScalafixPlugin.scala:437:20 
  [error] 437 |            (config / scalafix / streams).value.log,
  [error]     |             ^^^^^^^^
  [error]     |value / is not a member of sbt.ConfigKey, but could be made available as an extension method.
  [error]     |
  [error]     |One of the following imports might fix the problem:
  [error]     |
  [error]     |  import sbt.SlashSyntax0.given_Conversion_ConfigKey_RichConfiguration
  [error]     |  import sbt.given_Conversion_ConfigKey_RichConfiguration
  [error]     |

[bjaglin]

This was picked as significant indentation by the compiler (and has been also all along by scalafmt, as scala3 is aggressively/incorrectly used on all files as dialect), which was causing latestAvailable's type to be recursive ...