RFR: 8344703: Compiler Implementation for Flexible Constructor Bodies [v2]

[Maurizio Cimadamore]

> This PR finalizes the Flexible Constructor Bodies feature with no semantics changes.
> The main changes in this PR have to do with the various tests, which needed tweaking (e.g. to drop `@enablePreview` and fix corresponding golden files).
> 
> We might, later on, incorporate a fix for [this issue](https://bugs.openjdk.org/browse/JDK-8349754) into this PR, depending on where the specification for this feature lands.

Maurizio Cimadamore has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains two commits:

 - Merge branch 'master' into finalize_flex_constr_bodies
 - Initial push

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

Changes: https://git.openjdk.org/jdk/pull/24505/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24505&range=01
  Stats: 136 lines in 39 files changed: 1 ins; 39 del; 96 mod
  Patch: https://git.openjdk.org/jdk/pull/24505.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24505/head:pull/24505

PR: https://git.openjdk.org/jdk/pull/24505