[lworld] RFR: Merge jdk

[David Simms]

Merged jdk-15+19

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

Commit messages:
 - Merge tag 'jdk-15+19' into lworld_merge_jdk_15_19
 - 8242366: Fix JavaDoc warnings
 - 8242842: Avoid reallocating name when checking for trailing slash in ZipFile.getEntryPos
 - 8242629: Remove references to deprecated java.util.Observer and Observable
 - 8242597: Remove GenericTaskQueue<>::push_slow
 - 8241618: Fix trivial unchecked warnings for jdk.hotspot.agent
 - 8242485: Null _file checking in fileStream::flush()
 - 8242643: Shenandoah: split concurrent weak and strong root processing
 - 8242602: Shenandoah: allow earlier recycle of trashed regions during concurrent root processing
 - Merge
 - ...omitting 100 further commits.

The webrevs contain only the adjustments done while merging with regards to each parent branch:
 - lworld: https://webrevs.openjdk.java.net/valhalla/26/webrev.00.0
 - jdk: https://webrevs.openjdk.java.net/valhalla/26/webrev.00.1

Changes: https://git.openjdk.java.net/valhalla/pull/26/files
  Stats: 98590 lines in 895 files changed: 5101 ins; 91295 del; 2194 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/26.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/26/head:pull/26

PR: https://git.openjdk.java.net/valhalla/pull/26