feat(span): add `CompactStr::to_compact_string` method #15893

Job	Run time
Build Linter Benchmark	5m 30s
Benchmark (lexer)	1m 27s
Benchmark (parser)	1m 35s
Benchmark (transformer)	5m 56s
Benchmark (isolated_declarations)	1m 53s
Benchmark (semantic)	1m 35s
Benchmark (minifier)	2m 25s
Benchmark (codegen)	1m 29s
Benchmark (sourcemap)	1m 39s
Benchmark linter (0)	1m 49s
Benchmark linter (1)	1m 22s
Upload benchmarks	15s
	26m 55s

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