ref-filter: include reference to 'used_atom' within 'atom_value'

Ensure that each 'atom_value' has a reference to its corresponding
'used_atom'. This lets us use values within 'used_atom' in the
'handler' function.

Hence we can get the %(align) atom's parameters directly from the
'used_atom' therefore removing the necessity of passing %(align) atom's
parameters to 'atom_value'.

This also acts as a preparatory patch for the upcoming patch where we
introduce %(if:equals=) and %(if:notequals=).

Signed-off-by: Karthik Nayak <Karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: KarthikNayak

ref-filter.c

@@ -241,11 +241,9 @@ struct ref_formatting_state {
 
 struct atom_value {
 	const char *s;
-	union {
-		struct align align;
-	} u;
 	void (*handler)(struct atom_value *atomv, struct ref_formatting_state *state);
 	unsigned long ul; /* used for sorting when not FIELD_STR */
+	struct used_atom *atom;
 };
 
 /*
@@ -381,7 +379,7 @@ static void align_atom_handler(struct atom_value *atomv, struct ref_formatting_s
 	push_stack_element(&state->stack);
 	new = state->stack;
 	new->at_end = end_align_handler;
-	new->at_end_data = &atomv->u.align;
+	new->at_end_data = &atomv->atom->u.align;
 }
 
 static void if_then_else_handler(struct ref_formatting_stack **stack)
@@ -1090,6 +1088,7 @@ static void populate_value(struct ref_array_item *ref)
 		struct branch *branch = NULL;
 
 		v->handler = append_atom;
+		v->atom = atom;
 
 		if (*name == '*') {
 			deref = 1;
@@ -1154,7 +1153,6 @@ static void populate_value(struct ref_array_item *ref)
 				v->s = " ";
 			continue;
 		} else if (starts_with(name, "align")) {
-			v->u.align = atom->u.align;
 			v->handler = align_atom_handler;
 			continue;
 		} else if (!strcmp(name, "end")) {