all: ensure .git* files are standard across subprojects

Produced via:

```sh
zig run ./dev/ensure-standard-files.zig
```

Signed-off-by: Stephen Gutekanst <stephen@hexops.com>

gamemode/.gitattributes

@@ -0,0 +1,2 @@
+* text=auto eol=lf
+upstream/** linguist-vendored

gamemode/.github/FUNDING.yml

@@ -0,0 +1 @@
+github: slimsag

gamemode/.github/pull_request_template.md

@@ -0,0 +1,5 @@
+Please send your change to [the main repository](https://github.com/hexops/mach/tree/main/gamemode) instead, sorry for the trouble!
+
+This helps us avoid some complex merge conflicts we run into when changes are made to both repositories and history needs to be reconciled. Keeping PRs in just that repository enables us to use `git subtree` to trivially keep the two repositories in sync.
+
+Once your PR is merged over there, it'll automatically sync to this repository.

gamemode/.gitignore

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+# This file is for zig-specific build artifacts.
+# If you have OS-specific or editor-specific files to ignore,
+# such as *.swp or .DS_Store, put those in your global
+# ~/.gitignore and put this in your ~/.gitconfig:
+#
+# [core]
+#     excludesfile = ~/.gitignore
+#
+# Cheers!
+# -andrewrk
+
+zig-cache/
+zig-out/
+/release/
+/debug/
+/build/
+/build-*/
+/docgen_tmp/