Fixes https://github.com/flutter/flutter/issues/116070
Fixes https://github.com/flutter/flutter/issues/126202
Introduces `DlRegion` class which implements subset of `SkRegion`
required to get non-overlapping rectangles from region.
The implementation is different and faster than `SkRegion` for this
particular use-case (`display_list_region_benchmarks`):
Edit: Updated benchmark to latest revision and natively (initial run
went through rosetta)
```
----------------------------------------------------------------------------
Benchmark Time CPU Iterations
----------------------------------------------------------------------------
BM_RegionBenchmarkDlRegion/Tiny 616 us 616 us 908
BM_RegionBenchmarkSkRegion/Tiny 70559 us 70557 us 10
BM_RegionBenchmarkDlRegion/Small 1315 us 1314 us 537
BM_RegionBenchmarkSkRegion/Small 121736 us 121717 us 6
BM_RegionBenchmarkDlRegion/Medium 1079 us 1079 us 650
BM_RegionBenchmarkSkRegion/Medium 22039 us 22035 us 32
BM_RegionBenchmarkDlRegion/Large 399 us 399 us 1763
BM_RegionBenchmarkSkRegion/Large 1510 us 1510 us 466
```
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