docs(semantic): document `AstNode` and `AstNodes` #17594

Job	Run time
Build Linter Benchmark	2m 59s
Benchmark (lexer)	1m 20s
Benchmark (parser)	1m 50s
Benchmark (transformer)	2m 15s
Benchmark (isolated_declarations)	1m 43s
Benchmark (semantic)	1m 45s
Benchmark (minifier)	2m 17s
Benchmark (codegen)	1m 40s
Benchmark (sourcemap)	1m 50s
Benchmark linter (0)	2m 48s
Benchmark linter (1)	2m 21s
Upload benchmarks	28s
	23m 16s

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