Reimplement the ArgSplitter in Rust. #25053

Job	Run time
Classify changes	6s
Bootstrap Pants, test Rust (macOS13-x86_64)	18m 22s
Bootstrap Pants, test and lint Rust (Linux-x86_64)	13m 8s
Build wheels (Linux-ARM64)	0s
Bootstrap Pants, test Rust (Linux-ARM64)	16m 41s
Build wheels (Linux-x86_64)	0s
Build wheels (macOS13-x86_64)	0s
Ensure PR has release notes	3s
Build wheels (macOS14-ARM64)	0s
Test Python (Linux-x86_64) Shard 5/10	13m 47s
Test Python (Linux-x86_64) Shard 6/10	10m 58s
Test Python (Linux-x86_64) Shard 2/10	17m 14s
Lint Python and Shell	3m 59s
Test Python (Linux-x86_64) Shard 0/10	17m 56s
Test Python (Linux-x86_64) Shard 1/10	17m 31s
Test Python (Linux-x86_64) Shard 3/10	16m 25s
Test Python (Linux-x86_64) Shard 4/10	28m 4s
Test Python (Linux-x86_64) Shard 9/10	10m 49s
Test Python (Linux-x86_64) Shard 8/10	15m 53s
Test Python (Linux-x86_64) Shard 7/10	17m 46s
Test Python (Linux-ARM64)	13m 41s
Test Python (macOS13-x86_64)	22m 33s
Set Merge OK	1s
Merge OK	1s
	4h 14m 58s

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