Build for Minecraft 26.3

Adds 26.3 as a Stonecutter version, the last step of #39.

Input: 26.3 replaces GLFW with SDL, which numbers keys (scancodes),
modifiers and mouse buttons differently. Saturn keeps GLFW's numbers,
which common uses and the config's keybinds store, so saved keybinds
stay valid. The new Keys class converts at the boundary: key events,
modifiers and mouse buttons coming into Saturn's screens, and key codes
going to InputConstants. Its table pairs GLFW's codes with 26.3's
InputConstants of the same name. Key names come from the game on 26.3,
and version-specific code uses InputConstants' key constants rather
than GLFW's.

Rendering: Blaze3D's API moved to renderpearl, which Stonecutter
replacements cover. PoseStack's quaternion mulPose became rotate, and
TextureTarget takes a depth format instead of a flag. 26.3 compiles
shaders through SPIR-V and reorders the transforms block, so glass.fsh
takes explicit locations and the new order behind defines that
GlassRenderer sets, and the unlit cosmetics pipeline declares its
color target, which 26.3 requires.

OptionsScreen no longer takes whether a world is open.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

README.MD

@@ -18,7 +18,7 @@
 Saturn Client is a free, open-source Minecraft client designed to enhance the gameplay experience while staying lightweight and customizable.
 Our goal is to build a clean, optimized client that the community can contribute to and improve together.
 
-Saturn runs on Fabric and supports **Minecraft 1.21.4 to 1.21.11, 26.1 and 26.2**, with one build per version (the 26.1 build also runs on 26.1.1 and 26.1.2). If something doesn't work on your version, please open an issue.
+Saturn runs on Fabric and supports **Minecraft 1.21.4 to 1.21.11 and 26.1 to 26.3**, with one build per version (the 26.1 build also runs on 26.1.1 and 26.1.2). If something doesn't work on your version, please open an issue.
 
 ## Features