refactor(image): modernize GD image helper and fix minor handling inconsistencies

[joshtrichards]

• Resolves: #

Summary

Modernize OC\Image and simplify several code paths in the GD-backed image helper.

Alongside the cleanup, this also fixes a few minor behavioral inconsistencies in image loading/output and EXIF orientation handling.

Changes:

• tighten typing
• use match expressions where they improve readability
• drop docblocks already covered by the OCP\IImage interface
• add and improve class/property comments
• add docblocks to key internal functions
• simplify output and load paths to reduce branching and duplicated logic
• extract animated WebP detection into a dedicated helper
• tighten failure handling for unsupported or invalid image inputs
• improve EXIF/orientation handling and related return behavior
• eliminate some duplicate code and make future deduplication easier

Minor fixes included:

• fix WebP output so saving to a file uses the requested destination path (replaces fix(image): honor file path when saving WebP images #61598)
• make flip-only EXIF orientation fixes report success consistently
• align BMP handling with the validation/support checks used for other formats
• make base64 decoding/loading stricter and consistent with raw-data loading

This is primarily a refactor/cleanup of the existing image helper and does not change its overall responsibilities or public behavior beyond the minor fixes above.

TODO

• Explore existing test coverage gaps

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

AI (if applicable)

• The content of this PR was partly or fully generated using AI