Partial updates on remote textures

[ila-embsys]

Context

It is probably the relevant issue: zwin-project/zwin#17

The issue is slow texture updates. The slowing depend on a window size due to full window update instead of its partial damaged rectangles.

Summary

• Added new one function znr_gl_texture_sub_image_2d that maps to the glTexSubImage2D on a remote side. It is done with the same way as existed znr_gl_texture_image_2d that maps to the glTexImage2D.
• Added flags to the zn_view and the zn_view_child for indicating that a full texture was loaded, and it is ready for the partial updates.
• The main changes are done in zna_base_unit_read_wlr_texture. It checks the flag and does full texture update or partial.

How to check the behavior

1. Open Nautilus
2. Open a folder where is several items
3. Maximize the window
4. Move the cursor through the item list
5. Redrawing of selected items are queueing and finishes several seconds later after the cursor path. The request fixes it.