Use builtin generics and PEP 604 for type annotations wherever possible

[AlexWaygood]

I'm not sure if this is something we want to do or not -- but if it is something we want to do, this is what it looks like!

This PR was made using the following script, which relies on com2ann, pyupgrade, autoflake, pycln, black and isort all being installed:

import subprocess
from pathlib import Path

DIRECTORIES = ("mypy", "mypyc", "scripts", "misc", "docs")
BRANCH_NAME = "future-annotations"
BAD_TEST_FILE = "mypy/test/testinfer.py"


def run(*args, check: bool = True) -> None:
    subprocess.run(list(args), check=check)


def commit(message: str) -> None:
    run("git", "add", *DIRECTORIES)
    run("git", "commit", "-m", message)


def checkout_and_sync_with_master() -> None:
    run("git", "checkout", "master")
    run("git", "pull", "upstream", "master")
    run("git", "push")


def cleanup() -> None:
    run("git", "restore", "--staged", *DIRECTORIES)
    checkout_and_sync_with_master()


def main() -> None:
    checkout_and_sync_with_master()
    run("git", "branch", "-D", BRANCH_NAME, check=False)
    run("git", "checkout", "-b", BRANCH_NAME)

    for directory in DIRECTORIES:
        run("com2ann", directory)
    commit("Convert type comments to annotations using com2ann")

    for directory in DIRECTORIES:
        run("pyupgrade", *Path(directory).rglob("*.py"), check=False)
    commit("Apply pyupgrade")

    with open(BAD_TEST_FILE) as f:
        old = f.read()
    new = old.replace(
        "callee_kinds_: list[ArgKind | tuple[ArgKind, str]],",
        "callee_kinds_: list[ArgKind | Tuple[ArgKind, str]],",
    )
    with open(BAD_TEST_FILE, "w") as f:
        f.write(new)
    commit("Fix name collision in mypy/test/testinfer.py")

    for directory in DIRECTORIES:
        run("autoflake", "--in-place", *Path(directory).rglob("*.py"))
        run("pycln", "--all", "--exclude", r"mypyc/primitives/registry\.py", directory)
    commit("Remove unused imports using autoflake and pycln")

    run("black", ".")
    run("isort", ".")
    commit("black and isort")

    run("git", "push", "--set-upstream", "origin", BRANCH_NAME, "--force")


if __name__ == "__main__":
    try:
        main()
    finally:
        cleanup()

[JelleZijlstra]

Not related to your change but pretty sure this should be tuple[str, ...].

[AlexWaygood]

That looks highly plausible :) I'd rather not make that change in this PR, though

[jhance]

I prefer changing to this, it is less friction needing to import, and if we don't change the whole codebase over, using it in new code will be a style clash

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉

[AlexWaygood]

Thanks everybody! 🥳