RFR: Merge openjdk/jdk:master

[William Kemper]

This merges changes in PR#14856 (space info interface). The biggest change in resolving the conflicts is that `ShenandoahHeap` no longer implements the `ShenandoahSpaceInfo` interface. This functionality is now provided by `ShenandoahGeneration` and its derived classes.

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

Commit messages:
 - ShenandoahSpaceInfo is only implemented by ShenandoahGeneration now
 - Merge remote-tracking branch 'openjdk/master' into merge-jdk-pr-14856
 - 8311978: Shenandoah: Create abstraction over heap metrics for heuristics
 - 8312044: Simplify toolkit Builder/Writer world
 - 8312414: Make java.util.ServiceLoader.LANG_ACCESS final
 - 8136895: Writer not closed with disk full error, file resource leaked
 - 8309305: sun/security/ssl/SSLSocketImpl/BlockedAsyncClose.java fails with jtreg test timeout
 - 8312182: THPs cause huge RSS due to thread start timing issue
 - 8227229: Deprecate the launcher -Xdebug/-debug flags that have not done anything since Java 6
 - 8293114: JVM should trim the native heap
 - ... and 20 more: https://git.openjdk.org/shenandoah/compare/07450af0...88e15efb

The webrevs contain the adjustments done while merging with regards to each parent branch:
 - master: https://webrevs.openjdk.org/?repo=shenandoah&pr=302&range=00.0
 - openjdk/jdk:master: https://webrevs.openjdk.org/?repo=shenandoah&pr=302&range=00.1

Changes: https://git.openjdk.org/shenandoah/pull/302/files
  Stats: 19858 lines in 313 files changed: 9586 ins; 9714 del; 558 mod
  Patch: https://git.openjdk.org/shenandoah/pull/302.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/302/head:pull/302

PR: https://git.openjdk.org/shenandoah/pull/302