[ty] Add separate type for typevar "identity" (#20813) #55405

Job	Run time
pre-commit	1m 54s
mkdocs	2m 54s
Determine changes	14s
python package	1m 32s
cargo fmt	19s
cargo build (release)	15m 1s
cargo test (linux, release)	7m 17s
cargo clippy	1m 55s
cargo test (linux)	3m 9s
cargo build (msrv)	1m 57s
cargo test (wasm)	3m 21s
benchmarks instrumented (ruff)	6m 49s
check playground	-1s
cargo fuzz build	3m 51s
test scripts	1m 2s
formatter instabilities and black similarity	3m 3s
cargo test (windows)	6m 58s
ty completion evaluation	1m 36s
cargo shear	26s
benchmarks instrumented (ty)	9m 14s
benchmarks walltime (small\|large)	8m 6s
benchmarks walltime (medium\|multithreaded)	8m 26s
test ruff-lsp	53s
Fuzz for new ty panics	0s
fuzz parser	0s
ecosystem	0s
	1h 29m 56s

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