[DocsUI M3] Use GridDocumentHolder for photo picking

Previously there was a GridPhotoHolder class for image grid items
in photo picking mode (e.g. ACTION_OPEN_DOCUMENT intent with
"image/*" Mime type), which creates style inconsistencies
especially when images and directories are shown together. To
enforce style consistency, this CL stops using GridPhotoHolder
and all specific setup for grid photo picking and use
GridDocumentHolder instead, same as other grid items.

Note: previously in GridPhotoHolder there's no selection region,
after replacing to GridDocumentHolder it has the same selection
region logic as other items for consistency.

Check the attached bug for the before/after comparison.

Bug: 401107792
Test: m DocumentsUIGoogle && manual inspection
Flag: com.android.documentsui.flags.use_material3
Change-Id: I2ba8b8157ff13949875350914269718db55714ce