Trying to integrate 'constraint-layout'

Nobody has claimed this yet.

The docs talk about using a 'constraint solver' like Cassowary with the space layout to do constrained layout. [There is a discussion here](https://8th-dev.com/forum/index.php/topic,2228.0.html) on my forum about the matter.

TL;DR: Nuklear outputs coordinates as soon as e.g. nk_button_label() is called. But the constraint-solver doesn't know the coordinates until after all items with constraints have been added.

One solution might be to layout rectangles separately and solve the constraints, then apply the rectangles to the items. But that doesn't work unless you already know the minimum sizes of the items being inserted in those rectangles (e.g. text length of a button).

My idea is to add something like "nk_layout_constrained_begin" and "nk_layout_constrained_end" and have the solver work on 'end'... but how do I queue up the items added and act appropriately?

All ideas welcome!

Start by reading the Nuklear layout documentation and the discussion linked in the issue, then trace how nk_button_label() emits coordinates. The issue does not name a file or test, and completion criteria remain unresolved because the constrained-layout API and item-queueing approach are still open design questions.

Written by the indexing model from the issue text.