pw_preprocessor: Rename macro_arg_count.h

- Rename macro_arg_count.h to arguments.h
- Have macro_arg_count.h #include the renamed header for compatibility.

Change-Id: I781a457af88c6dd63ab8f8394bfe45cff9bc71e9
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/17500
Reviewed-by: Alexei Frolov <frolv@google.com>
Commit-Queue: Wyatt Hepler <hepler@google.com>
diff --git a/pw_preprocessor/BUILD b/pw_preprocessor/BUILD
index 439e383..d0d14d7 100644
--- a/pw_preprocessor/BUILD
+++ b/pw_preprocessor/BUILD
@@ -30,9 +30,9 @@
 )
 
 TESTS = [
+    "arguments_test",
     "boolean_test",
     "concat_test",
-    "macro_arg_count_test",
     "util_test",
 ]