Handle new profile form in migrate_settings and migrate_language_setting

[JosephTLyons]

I noticed that there are helper migration functions that apply settings transformations to multiple layers (root, platform, release-channel, and profile):

migrate_settings
migrate_language_setting

Both of these handle the old settings profile forms, so I've updated them to handle either form, for usage in historical and future migrations.

Migration m_2026_04_10 actually introduced a wrapper function to provide to migrate_settings to handle both forms, which is what clued me into the fact that I missed these when I wrote the m_2026_04_01 originally (I didn't know they existed).

Self-Review Checklist:

• I've reviewed my own diff for quality, security, and reliability
• [N/A] Unsafe blocks (if any) have justifying comments
• [N/A] The content is consistent with the UI/UX checklist
• Tests cover the new/changed behavior
• Performance impact has been considered and is acceptable

Closes #ISSUE

Release Notes:

• N/A