[GDEF] Use a bit-set for representing mark-filtering-sets

[behdad]

HB does this.

Not cleaned up. Waiting for googlefonts/fontations#1600

3% speedup in NotoNastaliqUrdu benchmark.

[behdad]

I see 2% slowdown in NotoNastaliq; whereas in HB we don't see a slowdown. I still suggest we take it, since it improves NotoSansDuployan mega-font by over 10% in both HB & HR, even though we currently don't shape that font correctly.

First need to sort out no_std though.

[behdad]

I see 2% slowdown in NotoNastaliq; whereas in HB we don't see a slowdown.

This might be because the HB BitSet has more optimizations than Fontations U32Set. In particular, in HB we keep the last page accessed cached, to avoid a bsearch into the (granted, very small) page_map.

[behdad]

3% speedup in NotoNastaliqUrdu benchmark.

My benchmarks are a bit off today. I'll do better benchmarking another day.

[behdad]

This is the last remaining optimization in HB that isn't yet in HR. We should update it and measure again.