RFR: 8334757: AssertionError: Missing type variable in where clause

[Liam Miller-Cushon]

Please consider this fix for [JDK-8334757](https://bugs.openjdk.org/browse/JDK-8334757).

This adds a missing case to argument preprocessing in `RichDiagnosticFormatter` to handle the `JCDiagnostic.AnnotatedType` wrapper types, which avoids a crash when types with type variables appear as arguments for diagnostics that use `JCDiagnostic.AnnotatedType`.

The wrapper type was introduced by [JDK-8291643](https://bugs.openjdk.org/browse/JDK-8291643) and is only used by the diagnostics introduced in [JDK-8043226](https://bugs.openjdk.org/browse/JDK-8043226), so backing out JDK-8043226 could also be considered.

-------------

Commit messages:
 - 8334757: AssertionError: Missing type variable in where clause

Changes: https://git.openjdk.org/jdk/pull/19840/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19840&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8334757
  Stats: 24 lines in 3 files changed: 24 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/19840.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19840/head:pull/19840

PR: https://git.openjdk.org/jdk/pull/19840