GTK3: Anchor autosizing

Original Reporter info from Mantis: crlab @neurolabusc1

• Reporter name: Chris Rorden

Description:

Anton's recent GTK3 patches have made huge strides in usability for many applications.

I note a few outstanding issues. These can be seen with my MRIcroGL github project, but I provide a simpler project below to demonstrate:

1. TSpinEdit spinner width ignored for anchoring (e.g. "color" button should be to the left of the "width" spin edit.
   
2. Button size not accurate (note overlap for L/A/P/R buttons, though note improved if buttons have AutoSize := true
   
3. Toggling visibility of components can lead to errors: Press the "Options" button a few times to show/hide boxes: not that the "Lines" and "Cutout" group boxes overlap. This is fixed if the user interactively resizes the form. Perhaps hiding/showing components requires some resize/refresh call.

Note: This issue is related to and extends issue 0036826 with a better example. If that issue is set to fixed, I will close it.

Mantis conversion info:

• Mantis ID: 36942
• OS: Ubuntu
• OS Build: 20.04
• Build: svn 63042
• Platform: Ryzen 3900X
• Version: 2.1 (SVN)
• Fixed in revision: 63911 (#86323528)
• Monitored by: » AntonK (Anton Kavalenka)