ref-filter: move code from 'for-each-ref'

Move most of the code from 'for-each-ref' to 'ref-filter' to make
it publicly available to other commands, this is to unify the code
of 'tag -l', 'branch -l' and 'for-each-ref' so that they can share
their implementations with each other.

Add 'ref-filter' to the Makefile, this completes the movement of code
from 'for-each-ref' to 'ref-filter'.

Mentored-by: Christian Couder <[email protected]>
Mentored-by: Matthieu Moy <[email protected]>
Signed-off-by: Karthik Nayak <[email protected]>
Reviewed-by: Matthieu Moy <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: KarthikNayak

Makefile

@@ -762,6 +762,7 @@ LIB_OBJS += reachable.o
 LIB_OBJS += read-cache.o
 LIB_OBJS += reflog-walk.o
 LIB_OBJS += refs.o
+LIB_OBJS += ref-filter.o
 LIB_OBJS += remote.o
 LIB_OBJS += replace_object.o
 LIB_OBJS += rerere.o