internal/uidriver/glfw: Avoid busy loop by sleeping

Updates hajimehoshi#1580

Update version to v2.2.0-alpha

Update version to v2.1.0-rc.1

ebiten: Guarantee that CursorPosition returns (0, 0) in the very init…

…ial state on desktops

This change also guarantees that CursorPosition always returns (0, 0)
on mobiles.

ebiten: Bug fix: Wrong documentation about SetScreenClearedEveryFrame

Closes hajimehoshi#1555

ebiten: Bug fix: Wrong documentation about SetScreenClearedEveryFrame

Closes hajimehoshi#1555

Skip the Wasm tests on Ubuntu

Skip the Wasm tests on Ubuntu

internal/uidriver/js: Bug fix: CursorMode didn't work on go2cpp

internal/graphics: Bug fix: Race condition at QuadVertices

QuadVertices or verticesBackend.slice reused its backend slice.
This caused a race condition. QuadVertices can be accessed from
multiple goroutines, and resetting the head and copying the data
at internal/graphicscommand might not be synced.

This change fixes this issue by basically reverting
9cb631e.

Closes hajimehoshi#1546