This adds support to show dots for the curves points when in edit mode,
using a specific overlay.
This also adds `DRW_curves_batch_cache_create_requested` which for now
only creates the point buffer for the newly added `edit_points` batch.
In the future, this will also handle other edit mode overlays, and
probably also replace the current curves batch cache creation.
Maniphest Tasks: T95770
Differential Revision: https://developer.blender.org/D14262
