Blender Git Loki

Fix T90026: attributes added in editmode are lost on modeswitch

When exiting editmode, customdata [and thus attributes] are copied from
**BMesh** to **Mesh** (in `BM_mesh_bm_to_me`).
When adding attributes, these were always added via
`CustomData_add_layer_named` only.
Instead (if we are in mesh editmode), we need to go through
`BM_data_layer_add_named` to properly update the **BMesh** (see
`update_data_blocks`) so we have stuff available to copy back to
**Mesh** when exiting editmode.
Same is done for removing (also going through BMesh).

This is now done, DomainInfo is updated to point to BMesh (instead of
Mesh) customdata when in editmode.

Maniphest Tasks: T90026

Differential Revision: https://developer.blender.org/D11998