Pre-commit: Allow adding downstream hooks without (less) risk of conflicts

Apply Godot copyright header only on the platform folders that we maintain upstream.
This lets downstream forks decide what to do with their potential proprietary platforms.

.pre-commit-config.yaml

@@ -146,6 +146,7 @@ repos:
         exclude: |
           (?x)^(
             core/math/bvh_.*\.inc$|
+            platform/(?!android|ios|linuxbsd|macos|web|windows)\w+/.*|
             platform/android/java/lib/src/com/.*|
             platform/android/java/lib/src/org/godotengine/godot/gl/GLSurfaceView\.java$|
             platform/android/java/lib/src/org/godotengine/godot/gl/EGLLogWrapper\.java$|
@@ -186,3 +187,15 @@ repos:
         language: python
         entry: python3 misc/scripts/dotnet_format.py
         types_or: [c#]
+
+# End of upstream Godot pre-commit hooks.
+#
+# Keep this separation to let downstream forks add their own hooks to this file,
+# without running into merge conflicts when rebasing on latest upstream.
+#
+# Start of downstream pre-commit hooks.
+#
+# This is still the "repo: local" scope, so new local hooks can be defined directly at this indentation:
+#     - id: new-local-hook
+# To add external repo hooks, bring the indentation back to:
+# - repo: my-remote-hook