ExifTool status report check silently missing on Drupal 11.3+ (#[LegacyRequirementsHook] suppresses hook_requirements() with no replacement)

Problem/Motivation

The module's hook_requirements() (in metadata_sanitizer.install) reports whether ExifTool is available on the Status report (/admin/reports/status). On Drupal 11.3+ this entry never appears, so site admins get no warning when ExifTool is missing/misconfigured.

Root cause: the function is annotated with #[\Drupal\Core\Hook\Attribute\LegacyRequirementsHook]. Per core's own docblock, that attribute prevents the procedural requirements hook from executing on 11.3.0+

Steps to reproduce

1. Install the module on Drupal 11.3+.
2. Go to Reports → Status report (/admin/reports/status).
3. Expected: an "ExifTool availability" row (OK if installed, Error if not).
4. Actual: no ExifTool row at all - even when ExifTool is missing.

Proposed resolution

Implement the modern hook and keep the legacy one for older cores, sharing one helper so there's a single ExifTool entry on every supported version (^10.3 || ^11):

- Add metadata_sanitizer_runtime_requirements(): array - invoked on 11.2/11.3+.
- Keep metadata_sanitizer_requirements($phase) with #[LegacyRequirementsHook] - runs on 10.3 / 11.0 / 11.1 (attribute unknown ⇒ it runs); suppressed on 11.3+.
- Both return the requirement under the same key (metadata_sanitizer_exiftool), so even if both fire on 11.2 they array_merge into a single entry - no duplicate.

While fixing this, the check can also be made accurate: the original hardcoded new Process(['exiftool', '-ver']), which relies on the web server PATH and ignores the module's configured executable_path (and the Runner's extra-dir resolution).

So a site with a custom path got a false "Not found." Recommend routing the check through the runner service (resolve the same executable used for sanitization) and reporting the resolved path + version.

Remaining tasks

- [ ] Add hook_runtime_requirements() + shared helper; keep the legacy hook for BC
- [ ] Functional test that loads /admin/reports/status and asserts the ExifTool row renders (regression guard, since direct function calls hide the bug)
- [ ] Confirm severity passes correctly: int REQUIREMENT_OK/REQUIREMENT_ERROR still work on 11.3 (core maps them to the RequirementSeverity enum) and are kept for 10.3 BC

User interface changes

API changes

Data model changes