RFR: Merge lworld

[David Simms]

Merge tag 'jdk-16+19'

Merge branch 'lworld' into type-restrictions_merge_16_19

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Commit messages:
 - Merge branch 'lworld' into type-restrictions_merge_16_19
 - Merge jdk
 - 8252324: Signal related code should be shared among POSIX platforms
 - 8216497: javadoc should auto-link to platform classes
 - 8253874: [JVMCI] added test omitted in 8252881
 - 8253475: Javadoc clean up in HttpExchange and HttpServer
 - 8253000: Remove redundant MAKE_SUBDIR argument
 - 8252997: Null-proofing for linker_md.c
 - 8254141: Typo in copyright year
 - 8249095: tools/javac/launcher/SourceLauncherTest.java fails on Windows
 - ... and 275 more: https://git.openjdk.java.net/valhalla/compare/3f60fc1b...d0d81c2d

The webrevs contain the adjustments done while merging with regards to each parent branch:
 - type-restrictions: https://webrevs.openjdk.java.net/?repo=valhalla&pr=217&range=00.0
 - lworld: https://webrevs.openjdk.java.net/?repo=valhalla&pr=217&range=00.1

Changes: https://git.openjdk.java.net/valhalla/pull/217/files
  Stats: 77268 lines in 3018 files changed: 28030 ins; 37423 del; 11815 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/217.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/217/head:pull/217

PR: https://git.openjdk.java.net/valhalla/pull/217