RFR: Merge jdk16

[Jesper Wilhelmsson]

Forwardport JDK 16 -> JDK 17

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

Commit messages:
 - Merge
 - 8258643: [TESTBUG] javax/swing/JComponent/7154030/bug7154030.java failed with "Exception: Failed to hide opaque button"
 - 8259574: SIGSEGV in BFSClosure::closure_impl
 - 8259641: C2: assert(early->dominates(LCA)) failed: early is high enough

The webrevs contain the adjustments done while merging with regards to each parent branch:
 - master: https://webrevs.openjdk.java.net/?repo=jdk&pr=2137&range=00.0
 - jdk16: https://webrevs.openjdk.java.net/?repo=jdk&pr=2137&range=00.1

Changes: https://git.openjdk.java.net/jdk/pull/2137/files
  Stats: 99 lines in 5 files changed: 95 ins; 1 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2137.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2137/head:pull/2137

PR: https://git.openjdk.java.net/jdk/pull/2137