RFR: Merge lworld [v2]

[Vicente Romero]

> Merge branch 'lworld' into bworld_merge_lworld
> # Conflicts:
> #	test/hotspot/jtreg/compiler/valhalla/inlinetypes/TestArrays.java
> #	test/hotspot/jtreg/runtime/valhalla/inlinetypes/FlattenableSemanticTest.java
> #	test/jdk/valhalla/valuetypes/MethodHandleTest.java
> #	test/jdk/valhalla/valuetypes/NullRestrictedTest.java
> #	test/jdk/valhalla/valuetypes/ValueObjectMethodsTest.java

Vicente Romero has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 121 commits:

 - Merge branch 'lworld' into bworld_merge_lworld
   
   # Conflicts:
   #	test/hotspot/jtreg/compiler/valhalla/inlinetypes/TestArrays.java
   #	test/hotspot/jtreg/runtime/valhalla/inlinetypes/FlattenableSemanticTest.java
   #	test/jdk/valhalla/valuetypes/MethodHandleTest.java
   #	test/jdk/valhalla/valuetypes/NullRestrictedTest.java
   #	test/jdk/valhalla/valuetypes/ValueObjectMethodsTest.java
 - javac should not place initializers of null restricted fields before the super invocation
   
   Reviewed-by: liach
 - Merge lworld
 - fixing bug in null checks generation
   
   Co-authored-by: Jan Lahoda <jlahoda at openjdk.org>
   Reviewed-by: jlahoda
 - Removing commented tests
 - Merge lworld
 - Classfile signature bang support
   
   Reviewed-by: mcimadamore
 - add different flavors to the useSiteNullChecks compiler option
   
   Reviewed-by: mcimadamore
 - Minor cleanup, preview and since
   
   Reviewed-by: vromero
 - add use site null checks for fields
   
   Reviewed-by: liach, mcimadamore
 - ... and 111 more: https://git.openjdk.org/valhalla/compare/2ad3ce16...99688b82

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

Changes: https://git.openjdk.org/valhalla/pull/2015/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=2015&range=01
  Stats: 7788 lines in 115 files changed: 7457 ins; 62 del; 269 mod
  Patch: https://git.openjdk.org/valhalla/pull/2015.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/2015/head:pull/2015

PR: https://git.openjdk.org/valhalla/pull/2015