Migrate to sbt 2.0.9 and sbt-softwaremill 3.0.1

[pierscin]

• sbt 2.0.9, sbt-softwaremill 3.0.1
• removed sbt-projectmatrix (built into sbt 2)
• sbt-scalajs 1.16.0 -> 1.22.0 (sbt 2 compatible)
• Scala 2.13.14 -> 2.13.18 (required by scala-library pulled in by Scala.js 1.22)
• sbt-ide-settings: 1.1.0 -> 1.1.4, org.jetbrains -> org.jetbrains.scala
• common settings are now bare settings in build.sbt (applied to all subprojects in sbt 2)
• sbt 2 syntax adjustments (%%% -> %%, : _* -> *, slash syntax, License)
• put -release 8 explicitly in scalac options for Scala 2 on the JVM
• CI: setup-sbt v1.5.10, testFull instead of test, shut down the sbt server before ci-release
• scalafmt: scala3 dialect for *.sbt files