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 - https://github.com/bevyengine/bevy/pull/12982
• [ ] Add 2d opaque phase with depth buffer - https://github.com/bevyengine/bevy/pull/13069
• [ ] Enable binning for 2d opaque phase - https://github.com/bevyengine/bevy/pull/13091
• [ ] Add 2d alpha mask phase - No PR yet
• [ ] 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.