SDF text rendering buffer refactor

[wouterlucas]

Currently the SDF text render uses a double buffer along side the main color buffer, this results into double buffer swapping and excessive draw calls.

This results into high performance issues on low-end devices, where SDF is expected to be much faster the performance drops off quickly as the current approach generates a lot of overhead. Creating "lag" when the text is being rendered.

Possible changes:

• Concat the SDF buffer to the main color buffer
• Render SDF text to a texture and copy it in
• Leverage instance drawing for text to reduce text overhead

cc @erikhaandrikman