Missing Raylib APIs

[squk]

Creating this bug to track any APIs that exist in raylib but not raygpu(and that make sense to exist in raygpu)

Shader APIs:

• IsShaderValid
• UnloadShader

Image APIs:

• IsImageValid 90e9eaa
• ExportImage f58a5ba
• ImageDraw
• ImageColorReplace

Windowing APIs:

• IsWindowReady
• IsWindowFocused
• IsWindowState
• SetWindowState
• SetExitKey
• GetWindowPosition
• CloseWindow
• SetWindowTitle

Other:

• GetWorldToScreen2D
• GetScreenToWorld2D
• SetTraceLogCallback

All Gamepad APIs (e.g. IsGamepadButtonDown).

[Peter0x44]

Most of the Window ones probably also need SubWindow versions.