attr: use repo_settings_get_attributesfile_path() and update callers

The functions `bootstrap_attr_stack()` and `git_attr_val_system()`
retrieve the "core.attributes" file via `git_attr_global_file()`
which reads from global state `git_attributes_file`.

Update the related functions to retrieve "core.attributesfile" via
the new accessor function `repo_settings_get_attributesfile_path()`
This improves multi-repository behaviour and aligns with the goal of
libifying of Git.

Signed-off-by: Olamide Caleb Bello <belkid98@gmail.com>

Author: cloobTech

attr.c

@@ -919,8 +919,8 @@ static void bootstrap_attr_stack(struct index_state *istate,
 	}
 
 	/* home directory */
-	if (git_attr_global_file()) {
-		e = read_attr_from_file(git_attr_global_file(), flags);
+	if (repo_settings_get_attributesfile_path(istate->repo)) {
+		e = read_attr_from_file(repo_settings_get_attributesfile_path(istate->repo), flags);
 		push_stack(stack, e, NULL, 0);
 	}
 

builtin/var.c

@@ -72,7 +72,7 @@ static char *git_attr_val_system(int ident_flag UNUSED)
 
 static char *git_attr_val_global(int ident_flag UNUSED)
 {
-	char *file = xstrdup_or_null(git_attr_global_file());
+	char *file = xstrdup_or_null(repo_settings_get_attributesfile_path(the_repository));
 	if (file) {
 		normalize_path_copy(file, file);
 		return file;