MFC r350386, r350390

r350386:
Add v_inval_buf_range, like vtruncbuf but for a range of a file

v_inval_buf_range invalidates all buffers within a certain LBA range of a
file. It will be used by fusefs(5). This commit is a partial merge of
r346162, r346606, and r346756 from projects/fuse2.

Reviewed by: kib
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D21032

r350390:
Better comments for vlrureclaim

Sponsored by: The FreeBSD Foundation