Project: Default to include window borders

Borderless is unexpected on Linux, and explicitly discouraged by the
[Flathub Quality Guidelines][1]. This can still be toggled off from the
in-game options if players prefer.

[1]:
https://docs.flathub.org/docs/for-app-authors/metainfo-guidelines/quality-guidelines/#include-window-shadow-and-rounded-corners

project.godot

@@ -185,7 +185,6 @@ Steam="*res://addons/steam_api/steam.gd"
 
 window/size/width=1280
 window/size/height=720
-window/size/borderless=true
 window/size/test_width=1920
 window/size/test_height=1080
 window/stretch/mode="2d"