text: Fix `getCharBoundaries()` for 0-width characters #27001

Job	Run time
Paths filter	6s
Check dependencies	1m 23s
Test Rust stable / ubuntu-24.04	5m 59s
Test Rust stable / windows-latest	12m 6s
Test Rust ${{ matrix.rust_version }} / ${{ matrix.os }}	0s
Lints with Rust stable	3m 56s
Test Rust stable / macos-14	3m 20s
Lints with Rust beta	4m 58s
Test Rust nightly / ubuntu-24.04	8m 39s
Lints with Rust nightly	3m 38s
Test Rust beta / ubuntu-24.04	4m 32s
	48m 37s

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