RFR: 8369573: Add missing compile commands help documentation for the signature part of method patterns

[Daniel Lundén]

The documentation of the signature part of method patterns in `java -XX:CompileCommand=help` is missing. We should add it.

### Changeset
- Improve the documentation of signatures in `java -XX:CompileCommand=help`.

### Testing

- [GitHub Actions](https://github.com/dlunde/jdk/actions/runs/18500483034)
- `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/27818/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27818&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8369573
  Stats: 38 lines in 1 file changed: 30 ins; 3 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/27818.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27818/head:pull/27818

PR: https://git.openjdk.org/jdk/pull/27818