Tables: ability to get column width as well as bind a resize handler to the column

[v-ein]

---

name: Pull Request
about: Create a pull request to help us improve
title: Tables: ability to get column width as well as bind a resize handler to the column
assignees: ''

---

Description:
This PR adds the rectSize property to mvTableColumn, with rect width reflecting the actual column width (without cell padding, which horizontally doesn't belong to columns anyway), and rect height set to zero due to difficulties in obtaining table height.

It also adds event handling and an item_resize handler to table columns. As a side effect this also fixes #2587.

Concerning Areas:
ImGuiTableColumn is internal API in Dear ImGui and might change in future. We do use internal APIs here and there, looks like for column width it's worthwhile because some applications really need to get width and resize events without clumsy workarounds. Worst case if API changes, we'll find a new way to obtain the width.

[nvglucifer]

Great that visible handler also works (#2587 ).
Can you add this for table indent also ?

[v-ein]

Great that visible handler also works (#2587 ).

Good catch! I completely forgot about that ticket - I'll add it to PR with the "closes" clause then.

Can you add this for table indent also ?

Maybe in a different PR - I don't want to mix things.