refactor: replace legacy icon classes in apps already on Vue 3

[skjnldsv]

Summary

Same as #65536 for the apps that are already on Vue 3, one commit per app: icon-loading* becomes NcLoadingIcon, the other icon-* classes become MDI icons.

• comments: spinners on first load, loading more, and editing or deleting a comment
• updatenotification: spinner, collapse arrows of the app lists, info icon on the changelog link
• user_status: spinner of the predefined statuses
• weather_status: pencil on the custom address input
• settings: rename, revoke and wipe actions of app passwords
• files: the "Creating file" overlay of the template picker
• core: filter actions and "Load more results" spinner of the legacy unified search

Two of these were broken since the Vue 3 migrations. The template picker overlay was empty, because NcEmptyContent has no icon prop and no default slot anymore in nextcloud-vue 9. The "Load more results" spinner never showed: the view passed :iconClass while LegacySearchResult only has an icon prop, and loadMore() never set the loading state in the first place. Neither is on stable35, so no backport.

What's left out: icon-user in the comments mention data, since NcRichContenteditable requires an icon class there, and the result icons of the legacy unified search, which come as classes from the search providers.

	Before	After
Template picker, creating a file
Legacy search, loading more
Legacy search, filters
Update, checking apps
Update, app lists
Update, up to date
Status message
Weather, custom address
App password actions

No screenshot for comments: the Comments sidebar tab doesn't load comments at all right now, that's a separate bug.

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

👾 This pull request was assisted by Claude Code, commits carry an Assisted-by trailer.