RFR: 8369569: Rename methods in regmask.hpp to conform with HotSpot coding style

[Daniel Lundén]

A number of methods in regmask.hpp do not conform with the HotSpot coding style. We should make sure they do.

### Changeset
- Rename methods in `regmask.hpp` to conform with HotSpot coding style.
- Similarly rename directly related methods in `chaitin.hpp`.
- Rename the constant register masks `All` and `Empty` to `ALL` and `EMPTY`.
- Fix a few additional code style issues at lines touched by the changeset.

Note: this is a syntax-only changeset (no functional changes).

### Testing

- [GitHub Actions](https://github.com/dlunde/jdk/actions/runs/18500704336)
- `tier1` and HotSpot parts of `tier2` and `tier3` (and additional Oracle-internal testing) on Windows x64, Linux x64, Linux aarch64, macOS x64, and macOS aarch64.

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Commit messages:
 - Fix issue

Changes: https://git.openjdk.org/jdk/pull/27817/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27817&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8369569
  Stats: 624 lines in 31 files changed: 12 ins; 0 del; 612 mod
  Patch: https://git.openjdk.org/jdk/pull/27817.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27817/head:pull/27817

PR: https://git.openjdk.org/jdk/pull/27817