[upstream_utils] Use pathlib instead of os.path (#7983)

A noteworthy change is the replacement of the `dp.startswith(os.path.join(".", "subdir"))` pattern. pathlib doesn't offer something with similar semantics besides `match` and `full_match`, so there's now a helper function that replicates the behavior.

Other notable changes include the addition of type annotations to ensure code correctness, using == to check file names instead of `endswith` for clarity (`endswith` is still used to check extensions), manual walking and copying being refactored in googletest, json, memory, nanopb, protobuf, and sleipnir to use `walk_cwd_and_copy_if`, and matching functions being shortened to the point where they can just be inlined into the lambda.

Co-authored-by: Tyler Veness <calcmogul@gmail.com>
Co-authored-by: David Vo <auscompgeek@users.noreply.github.com>

upstream_utils/argparse_lib.py

@@ -1,18 +1,17 @@
 #!/usr/bin/env python3
 
-import os
 import shutil
+from pathlib import Path
 
 from upstream_utils import Lib
 
 
-def copy_upstream_src(wpilib_root):
-    wpiutil = os.path.join(wpilib_root, "wpiutil")
+def copy_upstream_src(wpilib_root: Path):
+    wpiutil = wpilib_root / "wpiutil"
 
     # Copy header into allwpilib
-    dest_filename = os.path.join(
-        wpiutil,
-        f"src/main/native/thirdparty/argparse/include/wpi/argparse.h",
+    dest_filename = (
+        wpiutil / f"src/main/native/thirdparty/argparse/include/wpi/argparse.h"
     )
     shutil.copyfile("include/argparse/argparse.hpp", dest_filename)
     # Rename namespace from argparse to wpi