ext4: Convert pagecache_read() to use a folio

Use the folio API and support folios of arbitrary sizes.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Link: https://lore.kernel.org/r/20230324180129.1220691-29-willy@infradead.org


Signed-off-by: Theodore Ts'o <tytso@mit.edu>