Fixed STRETCHPIXELS flag not being exposed.

Fully revert ZDoom#2479

- this is version 4.13.0

- define dither shader in a way that is compatible with Apple's GLSL-…

…to-metal compiler

Reworked clientside lerping

Now acts as a rubberbanding effect. The result is that movement is now considered correct and adjusted towards the real position if not rather than cautiously moving towards the predicted position.

- version g4.13pre

Fixed local copies of items not respecting their Amount value

- version 4.12.0

- this is version 4.11.3