RFR: Merge jdk-15-ga

[Man Cao]

Hi all,

This PR is for a merge, and to demonstrate that non-Committer could help on merging/syncing via PRs.

Most significant merge conflicts are in hotspot.m4, and those changes have been moved to jvm-features.m4.
Tested with TSAN jtreg tests with LLVM 8.0.

We cannot test with LLVM 16.0, because jdk-15-ga itself does not build with LLVM 16.0. Also building bin/java with recent LLVM versions with `-fsanitizer=thread` would cause ThreadSanitizer:DEADLYSIGNAL error at run-time.

-Man

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Commit messages:
 - Merge tag 'jdk-15-ga' into tsan
 - 8246031: SSLSocket.getSession() doesn't close connection for timeout/ interrupts
 - 8251276: JDK-8248299 breaks JDK 15 validate-headers build
 - 8248299: two jdeps files miss copyright header
 - Added tag jdk-15+35 for changeset fd60c3146a02
 - 8249628: Remove EA from JDK 15 version string starting with Initial RC promotion
 - 8250609: C2 crash in IfNode::fold_compares
 - 8248597: [Graal] api/java_security/SignatureSpi/DelegationTests.html fails with Method "javasoft.sqe.tests.api.java.security.SignatureSpi.JCKSignatureSpi.clear" doesn't exist
 - 8250770: Net.java translateToSocketException does not handle IOException
 - Added tag jdk-15+34 for changeset b0817631d2f4
 - ... and 1861 more: https://git.openjdk.org/tsan/compare/5b22e180...47419566

The webrevs contain the adjustments done while merging with regards to each parent branch:
 - tsan: https://webrevs.openjdk.org/?repo=tsan&pr=15&range=00.0
 - jdk-15-ga: https://webrevs.openjdk.org/?repo=tsan&pr=15&range=00.1

Changes: https://git.openjdk.org/tsan/pull/15/files
  Stats: 2291107 lines in 15764 files changed: 1010028 ins; 1225411 del; 55668 mod
  Patch: https://git.openjdk.org/tsan/pull/15.diff
  Fetch: git fetch https://git.openjdk.org/tsan.git pull/15/head:pull/15

PR: https://git.openjdk.org/tsan/pull/15