What problem does this address?

Since we merged #47854, the width and height controls work independently of the aspect ratio control and it's not clear how they interact.

Here's a suggestion from @richtabor:

I'm thinking that if an aspect ratio is assigned, then the height/width should adhere to that ratio (regardless of which is changed). For example, if you set the aspect ratio to 16:10, then set a width of 1600px, the height should be auto-set to 1000px. And if you change the height to 800px, then the width would auto-set to 1280 (maintaining the 16:10 aspect ratio).

We could also leverage the existing link/unlink control to show that the values are linked together (and provide a way to unlink the height/width). If unlinked, then the aspect ratio value should no longer represent the chosen ratio, but rather "Freeform" (or another term if we prefer).