[upstream_utils] Refactor upstream_utils scripts (#4367)

* Root folder variable names are now more descriptive
* clone_repo() now restores the current working directory
* Removed setup_upstream_repo() since it's now identical to clone_repo()
* Moved am_patches()'s for loop into user scripts so the filename prefix
  doesn't need to be included in every patch filename
* Renamed am_patches() to git_am() since its only job now is to run "git am"
* Removed unused apply_patches() function
* Fixed typo in git_am()'s ignore_whitespace arg name

upstream_utils/update_eigen.py

@@ -5,10 +5,11 @@ import re
 import shutil
 
 from upstream_utils import (
-    setup_upstream_repo,
+    get_repo_root,
+    clone_repo,
     comment_out_invalid_includes,
     walk_cwd_and_copy_if,
-    am_patches,
+    git_am,
 )
 
 
@@ -102,12 +103,14 @@ def unsupported_inclusions(dp, f):
 
 
 def main():
-    root, repo = setup_upstream_repo("https://gitlab.com/libeigen/eigen.git", "3.4.0")
-    wpimath = os.path.join(root, "wpimath")
+    upstream_root = clone_repo("https://gitlab.com/libeigen/eigen.git", "3.4.0")
+    wpilib_root = get_repo_root()
+    wpimath = os.path.join(wpilib_root, "wpimath")
 
-    # Apply patches to original git repo
-    prefix = os.path.join(root, "upstream_utils/eigen_patches")
-    am_patches(repo, [os.path.join(prefix, "0001-Disable-warnings.patch")])
+    # Apply patches to upstream Git repo
+    os.chdir(upstream_root)
+    for f in ["0001-Disable-warnings.patch"]:
+        git_am(os.path.join(wpilib_root, "upstream_utils/eigen_patches", f))
 
     # Delete old install
     for d in [