fusefs: evict invalidated cache contents during write-through

fusefs: evict invalidated cache contents during write-through

fusefs's default cache mode is "writethrough", although it currently works
more like "write-around"; writes bypass the cache completely.  Since writes
bypass the cache, they were leaving stale previously-read data in the cache.
This commit invalidates that stale data.  It also adds a new global
v_inval_buf_range method, like vtruncbuf but for a range of a file.

PR:		235774
Reported by:	cem
Sponsored by:	The FreeBSD Foundation