Revamp badge measurement

[idg10]

There are some problems with the badge measurement code:

1. because it uses the system font support, it ends up loading the entire font directory just to look at the metrics for 1 font, which is clobbering our cold start time
2. I think this gives us a System.Drawing dependency which will stop us from running on Linux in the long run
3. the imaging library we were using to read this stuff might not longer be available in open source form

The best way to fix the cold start problems would be to extract the metrics for the font we use at build time and code-gen them into an embedded ReadOnlySpan<...> type array. This would absolutely minimize the startup costs. But there may be simpler ways that get us most of the way there.