dirstate-entry: add `modified` property This was already done in the Rust implementation and is a useful primitive. The C implementation had this called `merged`, but wasn't used anywhere. It will be used in the next changeset.

debug: add debug-revlog-stats command Display statistics about revlogs in the store. Useful to get an approximate size of a repository, etc. More statistics will be added in the future.

typing: attempt to remove @overloads in the platform module for stdlib methods This is mostly successful, as examining util.pyi, posix.pyi, and windows.pyi after a pytype run shows that the type overloads for `oslink`, `readlink`, `removedirs`, `rename`, `split`, and `unlink` have been removed. (Some of these still have an @overload, but the differences are the variable names, not the types.) However, @overloads remain for `abspath` and `normpath` for some reason. It's useful to redefine these methods for the type checking phase because in addition to excluding str and PathLike variants, some of these functions have optional args in stdlib that aren't implemented in the custom implementation on Windows, and we want the type checking to flag that instead of assuming it's an allowable overload everywhere. One last quirk I noticed that I can't explain- `pycompat.TYPE_CHECKING` is always False, so the conditionals need to check `typing.TYPE_CHECKING` directly. I tried dropping the custom code for assigning `pycompat.TYPE_CHECKING` and simply did `from typing import TYPE_CHECKING` directly in pycompat.py, and used `pycompat.TYPE_CHECKING` for the conditional here... and pytype complained that `pycompat` doesn't have the `TYPE_CHECKING` variable.

typing: add trivial type hints to rest of the windows platform module Skipping the file wrappers for now because there's interplay with C code, and making them subclass `typing.BinaryIO_Proxy` confuses PyCharm a bit.