Introduce `try`/`await`/`unsafe` macro lexical contexts with unfolded sequence handling #135

Job	Run time
Run tests using swift-syntax-dev-utils (Linux)	23m 17s
Run tests using swift-syntax-dev-utils (Windows)	45m 7s
Validate generated code	2m 51s
Test / Linux (5.9 - jammy)	3m 58s
Test / Linux (5.10 - jammy)	3m 52s
Test / Windows (5.9 - windows-2022)	23m 38s
Test / Windows (6.0 - windows-2022)	13m 15s
Test / Linux (6.0 - jammy)	4m 15s
Test / Windows (nightly - windows-2019)	16m 31s
Test / Linux (nightly-main - jammy)	4m 41s
Test / Windows (nightly-6.1 - windows-2019)	14m 50s
Test / Linux (nightly-6.1 - jammy)	4m 41s
Soundness / API breakage check	0s
Soundness / Broken symlinks check	6s
Soundness / Documentation check	5m 15s
Soundness / Format check	39s
Soundness / License headers check	11s
Soundness / Python lint check	6s
Soundness / Shell check	32s
Soundness / Unacceptable language check	3s
Soundness / YAML lint check	3s
	2h 47m 51s

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