pagemap: add filemap_grab_folio()

pagemap: add filemap_grab_folio()

Patch series "Convert to filemap_get_folios_tag()", v5.

This patch series replaces find_get_pages_range_tag() with
filemap_get_folios_tag().  This also allows the removal of multiple calls
to compound_head() throughout.

It also makes a good chunk of the straightforward conversions to folios,
and takes the opportunity to introduce a function that grabs a folio from
the pagecache.

This patch (of 23):

Add function filemap_grab_folio() to grab a folio from the page cache.
This function is meant to serve as a folio replacement for
grab_cache_page, and is used to facilitate the removal of
find_get_pages_range_tag().

Link: https://lkml.kernel.org/r/20230104211448.4804-1-vishal.moola@gmail.com
Link: https://lkml.kernel.org/r/20230104211448.4804-2-vishal.moola@gmail.com
Signed-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>