RFR: 8351568: Improve source code documentation for PhaseCFG::insert_anti_dependences [v7]

[Daniel Lundén]

> The current documentation for `PhaseCFG::insert_anti_dependences` is difficult to follow and sometimes even misleading. We should ensure the method is appropriately documented.
> 
> ### Changeset
> 
> - Rename `PhaseCFG::insert_anti_dependences` to `PhaseCFG::raise_above_anti_dependences`. The purpose of `PhaseCFG::raise_above_anti_dependences` is twofold: raise the load's LCA so that the load is scheduled before anti-dependent stores, and if necessary add anti-dependence edges between the load and certain anti-dependent stores (to ensure we later "raise" the load before anti-dependent stores in LCM). The name `PhaseCFG::insert_anti_dependences` suggests that we only add anti-dependence edges. The name `PhaseCFG::raise_above_anti_dependences`, therefore, seems more appropriate.
> - Significantly add to and revise the source code documentation of `PhaseCFG::raise_above_anti_dependences`.
> - Add, move, and revise `assert`s in `PhaseCFG::raise_above_anti_dependences`, including improved `assert` messages in a few places.
> - In the main worklist loop of `PhaseCFG::raise_above_anti_dependences`:
>   - Clean up how we identify the search root (avoid mutation).
>   - Add a missing early exit for `Phi` nodes when `LCA == early`.
> 
> ### Testing
> 
> - [GitHub Actions](https://github.com/dlunde/jdk/actions/runs/14706896111)
> - `tier1` to `tier4` (and additional Oracle-internal testing) on Windows x64, Linux x64, Linux aarch64, macOS x64, and macOS aarch64.

Daniel Lundén has updated the pull request incrementally with one additional commit since the last revision:

  Update after comments from Christian

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/24926/files
  - new: https://git.openjdk.org/jdk/pull/24926/files/11e37390..aec59a15

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=24926&range=06
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=24926&range=05-06

  Stats: 34 lines in 1 file changed: 2 ins; 1 del; 31 mod
  Patch: https://git.openjdk.org/jdk/pull/24926.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24926/head:pull/24926

PR: https://git.openjdk.org/jdk/pull/24926