Latte improvements + Better unicode support in gfx pack code

[Exzap]

Aside from smaller refactoring and bug fixes, the bigger changes in this PR are:

• An attempt to streamline the Latte backend code for calculating slice/mip indices during texture creation and copy. There was a discrepancy where slice and mip index where calculated differently (and sometimes incorrectly) for newly created textures vs textures sourced from cache. This is a kind of risky core change that may break things, so testing is needed!
• Fixed an issue where shaders generated with CafeGLSL could fail to compile due to using an unsupported way of encoding texture coordinates into the texture sample instruction
• Refactored unicode handling for graphic packs. Fixes Graphic pack causes crash when emulator path contains accents #1018