UI jittering/flickering on fast window resize with `glow`

**Describe the bug**
When the window is resized at high speed, the UI starts to flicker/jitter.

**To Reproduce**
Steps to reproduce the behavior:
1. Run the eframe example.
2. Resize the window fast.

**Expected behavior**
For the elements of the UI to stay put during resizing

**Screenshots**
Here's a quick screen recording displaying the issue:

https://user-images.githubusercontent.com/25753364/142637840-cae07e3d-e756-4e67-a513-324244b4de72.mov

**Desktop (please complete the following information):**
- OS: MacOS Montery 12.0.1
- M1 Max SoC - if that's applicable at all

Start by running the eframe example and reproducing the flicker while resizing a window quickly on the reported desktop setup. Read the issue comments and the relevant eframe/egui resize path to identify where the jitter originates. Done means the UI elements remain stable during fast resizing and the behavior is verified against the reproduction steps.

Written by the indexing model from the issue text.