refactor(transformer): shared `VarDeclarations` #18624

Job	Run time
Benchmark (lexer)	1m 41s
Benchmark (parser)	2m 18s
Build Linter Benchmark	3m 2s
Benchmark (transformer)	2m 27s
Benchmark (isolated_declarations)	2m 7s
Benchmark (semantic)	2m 0s
Benchmark (minifier)	2m 41s
Benchmark (codegen)	1m 58s
Benchmark (sourcemap)	1m 33s
Benchmark linter (0)	2m 54s
Benchmark linter (1)	2m 2s
Upload benchmarks	31s
	25m 14s

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