[NTOSKRNL] Fix lazy writer for in-use VACB.

[NTOSKRNL] Fix lazy writer for in-use VACB.

Adjusting refcount and enabling lazy-write for pinned
VACB makes it actually more efficient, often purging
data to disk, reducing memory stress for the system.

This is required for defering writes.

This commit unfortunately (?) reverts a previous revert.

CORE-12081
CORE-14582
CORE-14313