Measure Stems across weight, width, optical size

Inspired by https://typedrawers.com/discussion/5274/integerstemfinder I thought it could be useful for fontquant to measure stem thickness progressions across a family's design space (especially weight, width, optical size) and compare that to common models of progressions. This might also be a QA task for fontspector, but it might be helpful to auto-detect oddities like https://fonts.google.com/specimen/Syne