[WIP] Async + shutdown

[CedricGuillemet]

WIP - Not ready for review yet

Continuation of #1141

This error with OpenGL

BGFX Texture validation: 0x01006762 'Requested texture width/height is above the `maxTextureSize` limit.' - Texture width x height requested 256 x 256 (Max: 0).
/home/vsts/work/1/s/build/_deps/bgfx.cmake-src/bx/include/bx/inline/error.inl(74): ASSERT isOk() -> Error: 0x01006762 `Requested texture width/height is above the `maxTextureSize` limit.`

Same issue as #1163

=> Fixed with a frame rendered just after setting the graphics device. Does this have an influence on the rest of the test?

[CedricGuillemet]

This was a test PR. Closing.