Fixes#4288.
- Default imports to THIRD_PARTY, so in effect we merge the FIRST_PARTY and THIRD_PARTY stubs. This means import order is no longer affected by whether typing_extensions is installed locally.
- Treat typing_extensions, _typeshed and some others as standard library modules.
Note that isort master is very different from the latest release; we'll have to do something
different if and when the next isort release comes out.
* json: mark keyword-only args
Technically only true for Python 3.6+, but I didn't feel like copying
over the whole file just for Python 3.5. Let me know and I can.
* json: remove encoding from loads
This has been ignored and deprecated since 3.1 and will be removed in 3.9
It no longer even shows up in inspect.signature (in 3.8 it emits the
deprecation warning based on kwargs)
* json: update whitelists
Fixes the following issues:
* Literals rather than ... for default values
* None rather than ... for default value of typed variable
* Literals rather than ... # type for top level constants
* # Foo rather than # type: Foo
* return value of init not set to None
This is the other half of fixing #1115.
Also fixed the stub for JSONDecodeError and made it only exist in 3.5+.
Didn't otherwise review the exact attributes and types in the package.
