RFR: 8355065: ConcurrentModificationException in RichDiagnosticFormatter [v3]

[Liam Miller-Cushon]

> Hi, please consider this fix for [JDK-8355065](https://bugs.openjdk.org/browse/JDK-8355065). RichDiagnosticFormatter is comparing type variables by their `toString` representation, and in this example the comparison fails due to type annotations. Replacing a call to `stripMetadataIfNeeded` with `stripMetadata` allows the comparison to succeed, and is consistent with the approach used in other parts of RichDiagnosticFormatter (e.g. for [the fix for JDK-8144580](https://github.com/openjdk/jdk/commit/570883e4dc5f769e17b3fcd8f2bbeb369dfe3a5d)).

Liam Miller-Cushon has updated the pull request incrementally with one additional commit since the last revision:

  EnumMap

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Changes:
  - all: https://git.openjdk.org/jdk/pull/24769/files
  - new: https://git.openjdk.org/jdk/pull/24769/files/1a1ff0bf..da1c2f50

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=24769&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=24769&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/24769.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24769/head:pull/24769

PR: https://git.openjdk.org/jdk/pull/24769