RFR: 8291643: Consider omitting type annotations from type error diagnostics

[Liam Miller-Cushon]

Hi,

Please consider this fix for [JDK-8291643](https://bugs.openjdk.org/browse/JDK-8291643), which causes javac to remove type-use annotations when formatting types in diagnostics.

For the example like the one in the bug, this change causes javac to emit the diagnostic like `incompatible types: List<String> cannot be converted to List<Number>` rather than `incompatible types: List<String> cannot be converted to List<@Nullable Number>`. Including the type annotations can be confusing, because they do not impact the type checking done by the compiler.

An alternative I considered was to remove type annotations from types for specific diagnostics, instead of doing it unconditionally in diagnostic formatting. I can revisit that if the current approach seems too broad.

The test update to `test/langtools/tools/javac/lambda/LambdaConv25.out` is because a `ForAll` is being formatted, and `stripMetadata()` uses a `StructuralTypeMapping` which rewrites away the `ForAll`.

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Commit messages:
 - 8291643: Consider omitting type annotations from type error diagnostics

Changes: https://git.openjdk.org/jdk/pull/16578/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16578&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8291643
  Stats: 29 lines in 5 files changed: 23 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/16578.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16578/head:pull/16578

PR: https://git.openjdk.org/jdk/pull/16578