RFR: 8335136: Underscore as parameter name in one-parameter functional types fails to compile

[Evemose]

Seems like this bug been around for quite a bunch of time now. Basically, in JavacParser, UNDERSCORE case havent been present in block parsing switch statement, so it was treated as default and it wasnt recognized as part of yield statement. This simple fix adds UNDERSCORE case right next to IDENTIFIER case to solve this problem. Syntax like yield _ = 3 is still invalid.

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Commit messages:
 - Merge branch 'openjdk:master' into underscore-fails-as-lambda-param-in-yield
 - actual bug number
 - remove ^M
 - test
 - init

Changes: https://git.openjdk.org/jdk/pull/19878/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19878&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8335136
  Stats: 137 lines in 2 files changed: 136 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/19878.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19878/head:pull/19878

PR: https://git.openjdk.org/jdk/pull/19878