Treat `typing.Annotated` subscripts as type definitions #25476

Job	Run time
cargo fmt	18s
Determine changes	10s
pre-commit	42s
mkdocs	2m 5s
python package	1m 20s
cargo test (linux)	4m 2s
benchmarks	4m 36s
cargo fuzz	5m 26s
cargo clippy	1m 51s
cargo test (wasm)	1m 18s
cargo test (windows)	7m 40s
cargo udeps	2m 4s
formatter instabilities and black similarity	0s
test scripts	58s
ecosystem	8m 23s
test ruff-lsp	20s
	41m 13s

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