This allows us to upgrade freetype beyond 2.9.1 (actually, 2.8.1 due to a bug in freetype 2.9) without wildly different font metrics. The reason that we don't want to change font metrics algorithms is that freetype's new algorithm is very different than the algorithm used for SWF fonts. The older freetype algorithm is closer to SWF, so we want to stick with it.
Thankfully, freetype supports accessing various metrics stored in font files in a more raw form, so we can provide our own custom algorithm in a way that is fully supported by freetype. I just copied the existing algorithm straight from 2.9.1 to restore our preferred behavior.
I confirmed that, after this change, OpenFL renders metrics like Lime 8.1.3. But we have the same upgraded freetype as Lime 8.2.0 that we had to revert for 8.2.1.
I plan to experiment with a mode that matches SWF even more closely, now that I have a better understanding of how fonts and freetype work.
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