RFR: 8370220: C2: rename methods and improve documentation around get_ctrl and idom lazy updating/forwarding of ctrl and idom via dead ctrl nodes [v10]

[Emanuel Peter]

> When working on https://github.com/openjdk/jdk/pull/27889, I was irritated by the lack of documentation and suboptimal naming.
> 
> Here, I'm doing the following:
> - Add more documentation, and improve it in other cases.
> - Rename "lazy" methods: "lazy" could indicate that we delay it somehow until later, but it is unclear what is delayed.
>   - `lazy_replace` -> `replace_ctrl_node_and_forward_ctrl_and_idom`
>   - `lazy_update` -> `install_lazy_ctrl_and_idom_forwarding`
> - Made some methods private, and added some additional asserts.
> 
> I'd be more than happy for even better names, and suggestions how to improve the documentation further :)
> 
> Related issues:
> https://github.com/openjdk/jdk/pull/27889
> https://github.com/openjdk/jdk/pull/15720

Emanuel Peter has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 19 additional commits since the last revision:

 - Merge branch 'master' into JDK-8370220-get-ctrl-documentation
 - Merge branch 'JDK-8370220-get-ctrl-documentation' of https://github.com/eme64/jdk into JDK-8370220-get-ctrl-documentation
 - Apply suggestions from code review
   
   Co-authored-by: Christian Hagedorn <christian.hagedorn at oracle.com>
 - fix shenandoah replace for phis
 - renaming for Tobias
 - Apply suggestions from code review
   
   Co-authored-by: Tobias Hartmann <tobias.hartmann at oracle.com>
 - more for Christian part 3
 - more for Christian part 2
 - Apply suggestions from code review
   
   Co-authored-by: Christian Hagedorn <christian.hagedorn at oracle.com>
 - for Christian part 1
 - ... and 9 more: https://git.openjdk.org/jdk/compare/aa5cb3a4...e4bcb769

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/27892/files
  - new: https://git.openjdk.org/jdk/pull/27892/files/44e808bb..e4bcb769

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27892&range=09
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27892&range=08-09

  Stats: 14620 lines in 312 files changed: 8959 ins; 3739 del; 1922 mod
  Patch: https://git.openjdk.org/jdk/pull/27892.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27892/head:pull/27892

PR: https://git.openjdk.org/jdk/pull/27892