RFR: 8286797: Guards of constant value false are not permitted

Tue May 17 12:34:19 UTC 2022

Simple fix that addresses this line from the spec:

> It is a compile-time error if a when expression is a constant expression ([15.29](https://docs.oracle.com/javase/specs/jls/se18/html/jls-15.html#jls-15.29)) with the value false.

Extracts one small utility method `isBooleanWithValue` in `TreeInfo`.

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Commit messages:
 - 8286797: Guards of constant value false are not permitted

Changes: https://git.openjdk.java.net/jdk/pull/8745/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8745&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8286797
  Stats: 106 lines in 9 files changed: 100 ins; 0 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8745.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8745/head:pull/8745

PR: https://git.openjdk.java.net/jdk/pull/8745