Changes:
- Remove `BLI_memarena` (Use `MEM_cnew` and `MEM_delete` to allocate cached data)
- Implement `snap_object_data_mesh_free_ensure` and `snap_object_data_editmesh_free_ensure` and skip need to get original key Object for editmesh data
- Use `BMEditMesh` as key for editmesh `Ghash`
- Make a better distinction between `SnapObjectData`s. (`SnapData_Mesh` and `SnapData_EditMesh`)
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