Mesh2d improvements tracking issues

## Description

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

- [x] Clean up 2d render phases to prepare for adding more phases - https://github.com/bevyengine/bevy/pull/12982
- [x] Add 2d opaque phase with depth buffer - https://github.com/bevyengine/bevy/pull/13069
- [x] Enable binning for 2d opaque phase - https://github.com/bevyengine/bevy/pull/13091
- [x] Add 2d alpha mask phase - https://github.com/bevyengine/bevy/pull/14724
- [ ] Draw opaque/masked sprites in the opaque pass
- [ ] Make the 2d depth buffer optional
- [ ] Investigate ways to make transparent mesh2d as fast as sprites
- [ ] Investigate if using OIT with binning in 2d can speed up alpha blending compared to sprites.
- [ ] ~~Investigate using vertex pulling for all mesh2d~~
- [ ] Switch to using mesh2d as a backend for sprites