fix: resolve LogSource for getClass results on Scala 3 - #3609

Motivation:
On Scala 3, `Logging(system, getClass)` fails to compile with
"Cannot find LogSource for Class[? <: Foo]". `getClass` returns a
wildcard class type, which Scala 3 does not match against
`LogSource.fromAnyClass[T]: LogSource[Class[T]]`. Scala 2.13 accepts it.

Modification:
- Make `object LogSource` extend a new `LogSourceCompat` trait.
- The Scala 3 `LogSourceCompat` adds a lower priority
  `fromAnySubClass[T]: LogSource[Class[? <: T]]` implicit; the Scala 2.13
  version is empty because Scala 2 reports that implicit as ambiguous
  with `fromAnyClass`.
- `fromAnyClass` is unchanged; changing its signature instead fails MiMa
  with an IncompatibleSignatureProblem.
- Add `LogSourceSpec`.

Result:
`Logging(system, getClass)` and `LogSource(getClass, system)` compile
on Scala 3.

Tests:
- `actor-tests/Test/testOnly org.apache.pekko.event.LogSourceSpec` on
  Scala 3.3.8 without the fix: compile error "Cannot find LogSource for
  Class[? <: ...LogsWithGetClass]"
- `actor-tests/Test/testOnly org.apache.pekko.event.LogSourceSpec
  org.apache.pekko.event.LoggerSpec` with the fix: passed on 2.13.18
  and 3.3.8
- `actor/mimaReportBinaryIssues`: passed on 2.13.18 and 3.3.8
- scalafmt run on changed files

References:
Fixes apache#1538