Fix T65918 DRW: Crash when add a any modifier to a curve

Cleanup: GPU: Fix codestyle

Fix T65631 Eevee: Translucent shader broken in Eevee when AO is enabled

MeshBatchCache: Speedup: Do not return valid batch if geometry is empty

There was a huge overhead of batches that had no geometry. The loose
wire batch was the culprit.

Fix T65689 Geometry overlaps axis selector

It seems that in 2.79 callbacks were drawn with depth test off by default.

Fix T65805 Assert "Too many draw engines enabled at the same time"

Fix T57650 UVEdit: selection not visible if behind unselected UVs

Use depth buffer to order the uv edges correctly to always draw selected
edges on top.
We still use the double drawing workaround for points to keep the smooth
antialiased display.

DRW: Make stencil state clearer and distinct

Write and test states are now separate and need to be explicit.

Also add asserts when trying to write without test enabled.

Fix T65569 Eevee: Volumetrics on alphablend surf. not working in renders

The wrong volume buffer was used one frame out of two.

Cleanup: DRW: Remove one useless matrix multiplication