hex-ll: separate out non-hash-algo functions

hex-ll: separate out non-hash-algo functions

In order to further reduce all-in-one headers, separate out functions in
hex.h that do not operate on object hashes into its own file, hex-ll.h,
and update the include directives in the .c files that need only such
functions accordingly.

Signed-off-by: Calvin Wan <calvinwan@google.com>
Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>