path.c: migrate global git_path_* to take a repository argument

Migrate all git_path_* functions that are defined in path.c to take a
repository argument. Unlike other patches in this series, do not use the
 #define trick, as we rewrite the whole function, which is rather small.

This doesn't migrate all the functions, as other builtins have their own
local path functions defined using GIT_PATH_FUNC. So keep that macro
around to serve the other locations.

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

repository.h

@@ -38,6 +38,11 @@ struct repository {
 	/* The store in which the refs are held. */
 	struct ref_store *refs;
 
+	/*
+	 * Contains path to often used file names.
+	 */
+	struct path_cache cached_paths;
+
 	/*
 	 * Path to the repository's graft file.
 	 * Cannot be NULL after initialization.