Integrated: Merge lworld

[Vicente Romero]

Merge branch 'lworld' into jep_401_javac_merge_lworld
# Conflicts:
#	src/jdk.compiler/share/classes/com/sun/tools/javac/code/Preview.java
#	src/jdk.compiler/share/classes/com/sun/tools/javac/code/Source.java

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Commit messages:
 - Merge branch 'lworld' into jep_401_javac_merge_lworld
 - Merge lworld
 - 8324980: [lworld] removing dead code plus gratuitous differences with jdk/master
 - 8324864: [lworld] remove non-cyclic membership checks
 - 8194743: Compiler implementation for Statements before super()
 - 8324787: [lworld] eliminate restrictions on abstract value classes and additional refactorings
 - 8324784: [lworld] remove constant propagation code and tests
 - 8324643: [lworld] remove ACC_VALUE flag and the 'identity' modifier
 - 8324052: [lworld] remove experimental code from lworld

The merge commit only contains trivial merges, so no merge-specific webrevs have been generated.

Changes: https://git.openjdk.org/valhalla/pull/988/files
  Stats: 7473 lines in 257 files changed: 1915 ins; 4818 del; 740 mod
  Patch: https://git.openjdk.org/valhalla/pull/988.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/988/head:pull/988

PR: https://git.openjdk.org/valhalla/pull/988