Page cache changes for 5.19

 - Appoint myself page cache maintainer

 - Fix how scsicam uses the page cache

 - Use the memalloc_nofs_save() API to replace AOP_FLAG_NOFS

 - Remove the AOP flags entirely

 - Remove pagecache_write_begin() and pagecache_write_end()

 - Documentation updates

 - Convert several address_space operations to use folios:
   - is_dirty_writeback
   - readpage becomes read_folio
   - releasepage becomes release_folio
   - freepage becomes free_folio

 - Change filler_t to require a struct file pointer be the first argument
   like ->read_folio
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