feat(android): support Android 14 partial photo access

[jkmassel]

Summary

Layers on top of #510 with proper handling for Android 14's "Select photos and videos" partial-access flow.

Android 14 added a third option to the photo-permission dialog: users can pick Allow, Select photos and videos, or Don't allow. Without opting in to the partial-access permission, the system still shows the three-way prompt, but the app sees a partial grant as full access — and the user has no in-app way to update which photos they've shared. The strip would show the same 3 photos forever, with the only path to add more being a trip to system Settings.

This PR closes that gap.

Changes

• Declare READ_MEDIA_VISUAL_USER_SELECTED in the manifest. This is the partial-access opt-in that signals to the system that we understand and handle partial grants.

  Permission	SDK range	Purpose
  READ_MEDIA_VISUAL_USER_SELECTED	34+	Detect partial grants, expose a Manage tile

• Switch the launcher from RequestPermission to RequestMultiplePermissions, requesting both READ_MEDIA_IMAGES and READ_MEDIA_VISUAL_USER_SELECTED together via photosPermissions(): Array<String> (API-tiered). When partial is already granted, calling the launcher again reopens the photo picker so the user can update the selection — that's the in-app "Manage" path.

• hasPhotosPermission now accepts either full or partial reads. isPartialPhotoAccess distinguishes "selected photos only" so the strip can surface a Manage affordance.

• PhotoAccess.PartialAccess data class carries onManageSelection. PhotoAccess.Granted gains an optional partialAccess: PartialAccess? field — non-null only when the user picked partial.

• ManageSelectionTile sits right after the Photos/Camera column when partial access is active. Uses the Tune icon and secondaryContainer colour so it reads as an editorial control distinct from Photos/Camera. Visible without scrolling so partial-access users find it immediately.

• refreshTick keys the MediaStore re-query so a selection update (where granted stays true but the visible set changes) refreshes the strip — granted / limit alone wouldn't trigger that.

Test plan

Requires an Android 14+ device.

• First launch + tap Allow in the rationale → system shows three-way prompt → pick Select photos and videos → choose 2-3 photos → strip shows those photos plus a Manage tile after the Photos/Camera column.
• Tap Manage → system reopens the photo picker → add another photo → return → strip updates to include the new selection.
• Tap Manage → system reopens the photo picker → remove one photo → return → strip updates to reflect the smaller selection.
• In system Settings, change from partial to full access → return to the app → Manage tile disappears, full thumbnail strip remains.
• In system Settings, revoke entirely → return to the app → rationale card returns (sticky rejected flag was cleared on grant in the parent PR).
• On Android 13 (no READ_MEDIA_VISUAL_USER_SELECTED available) → partial-access path is unreachable. Granting READ_MEDIA_IMAGES works as before.
• PhotoAccessStateTest::partial access still shows full strip passes.
• ./gradlew :Gutenberg:detekt :Gutenberg:assembleDebug :Gutenberg:testDebugUnitTest passes.

[wpmobilebot]

XCFramework Build

This PR's XCFramework is available for testing. Add the following to your Package.swift:

.package(url: "https://github.com/wordpress-mobile/GutenbergKit", branch: "pr-build/511")

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