RFR: 8325805: Compiler Implementation for Flexible Constructor Bodies (Second Preview) [v9]

[Archie Cobbs]

> This patch changes the compiler to allow constructors to make assignments to fields prior to the `super()` invocation, i.e., in the pre-construction context.  This is part of the work associated with [JDK-8325803 - Flexible Constructor Bodies (Second Preview)](https://bugs.openjdk.org/browse/JDK-8325803).
> 
> This patch is based the relevant bits from @vicente-romero-oracle's commit [1b99b5cf](https://github.com/openjdk/valhalla/commit/1b99b5cfd9a5d484b9e7bdfc284daad9ad6535bf) to the valhalla repo.

Archie Cobbs has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 27 commits:

 - Merge branch 'master' into JDK-8325805
 - Update feature name "statements before super()" -> "flexible constructors".
 - Remove redundant type check.
 - Use instanceof instead of hasTag().
 - Refactor some common logic into new method Resolve.isEarlyReference().
 - Minor improvements to method name and Javadoc description.
 - Add assertion to Resolve.resolveSelf() verifying symbol name.
 - Allow declaring and instantiating local classes prior to super().
 - Merge branch 'master' into JDK-8325805
 - Merge branch 'master' into JDK-8325805
 - ... and 17 more: https://git.openjdk.org/jdk/compare/0a4eeeaa...963ca915

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

Changes: https://git.openjdk.org/jdk/pull/18088/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18088&range=08
  Stats: 566 lines in 18 files changed: 508 ins; 43 del; 15 mod
  Patch: https://git.openjdk.org/jdk/pull/18088.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18088/head:pull/18088

PR: https://git.openjdk.org/jdk/pull/18088