Fix source slicing for whitespace-stripping comments

[chancancode]

Re-apply #1430 with a more robust implementation and tests

Also turns the warning into a localAssert() so it gets stripped before reaching downstream consumers.

This relates to #1431 in that this removes the warning, so to the extent that #1431 was motivated by sliencing the warning in Ember builds, it avoids the issue. But I haven't investigated the root cause of that issue and whether it is indicative of an actual bug somewhere deeper.

Fixes emberjs/ember.js#19392

[github-actions]

	This PR	main
Dev	582K └─┬ . 169K ├── runtime 159K ├── syntax 100K ├── compiler 58K ├── opcode-compiler 27K ├── manager 19K ├── validator 11K ├── program 8.9K ├── reference 7.2K ├── destroyable 6.3K ├── util 4.3K ├── node 3.4K ├── global-context 2.5K ├── wire-format 1.0K ├── vm 969B ├── encoder 844B ├── vm-babel-plugins 606B └── owner	582K └─┬ . 169K ├── runtime 159K ├── syntax 100K ├── compiler 58K ├── opcode-compiler 27K ├── manager 19K ├── validator 11K ├── program 8.9K ├── reference 7.2K ├── destroyable 6.3K ├── util 4.3K ├── node 3.4K ├── global-context 2.5K ├── wire-format 1.0K ├── vm 969B ├── encoder 844B ├── vm-babel-plugins 606B └── owner
Prod	230K └─┬ . 69K ├── syntax 63K ├── runtime 48K ├── compiler 18K ├── opcode-compiler 7.9K ├── manager 4.8K ├── program 4.0K ├── validator 3.6K ├── reference 2.4K ├── util 2.1K ├── node 1.6K ├── wire-format 1.5K ├── destroyable 737B ├── vm 594B ├── global-context 516B ├── encoder 469B ├── vm-babel-plugins 155B └── owner	230K └─┬ . 69K ├── syntax 63K ├── runtime 48K ├── compiler 18K ├── opcode-compiler 7.9K ├── manager 4.8K ├── program 4.0K ├── validator 3.6K ├── reference 2.4K ├── util 2.1K ├── node 1.6K ├── wire-format 1.5K ├── destroyable 737B ├── vm 594B ├── global-context 516B ├── encoder 469B ├── vm-babel-plugins 155B └── owner

[NullVoxPopuli]

https://github.com/glimmerjs/glimmer-vm/actions/runs/13466445316/job/37633202706?pr=1717#step:4:5753

Same as on main, so we're good here 🎉

thanks for fixing this!