refactor(parser): shorten `UniquePromise` code (#5805) #17377

Job	Run time
Benchmark (lexer)	1m 27s
Build Linter Benchmark	2m 55s
Benchmark (parser)	1m 44s
Benchmark (transformer)	2m 6s
Benchmark (isolated_declarations)	1m 51s
Benchmark (semantic)	1m 47s
Benchmark (minifier)	2m 24s
Benchmark (codegen)	1m 36s
Benchmark (sourcemap)	1m 36s
Benchmark linter (0)	3m 25s
Benchmark linter (1)	2m 10s
Upload benchmarks	25s
	23m 26s

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