Mesh2d improvements tracking issues

[IceSentry]

Description

Mesh2d is currently very slow compared to sprites and is also missing quite a few features compared to 3d.

• Clean up 2d render phases to prepare for adding more phases - Clean up 2d render phases #12982
• Add 2d opaque phase with depth buffer - Add 2d opaque phase with depth buffer #13069
• Enable binning for 2d opaque phase - Use BinnedRenderPhase for Opaque2d #13091
• Add 2d alpha mask phase - No PR yet
• Make the 2d depth buffer optional
• Investigate using vertex pulling for all mesh2d
• Switch to using mesh2d as a backend for sprites
• Investigate if using OIT with binning in 2d can speed up alpha blending compared to sprites.