Generate the Python stubs automatically

[dgelessus]

Closes #1660. Adds a script to automatically generate the Python "stub" files under Scripts/Python/plasma. The script must be run from the in-game Python console:

>>> __import__("generate_stubs").run()

This will generate stubs for all Plasma built-in modules into a subfolder "plasma_stubs_generated" under the game folder.

Everything happens fully automatically using runtime introspection. Only one part is "semi-manual": because Python cannot introspect the signatures of C-defined functions, all function parameters must be specified manually in the C++-defined function docstrings, on a line starting with Params: . This convention was apparently used by Cyan originally, so most function docstrings already follow this format.

The generator itself is almost completely finished, but this PR still needs a bit of work:

• The generator currently removes all type annotations.
  • This will be mostly fixed by copying the parameter types from the existing stubs into the Params: lines in the C++-defined docstrings.
  • There's no way to specify type annotations for function return types and attribute/property types. Most likely, I'll implement this using another docstring line prefix, such as Returns: .
• Some C++-defined docstrings are outdated, incorrect, slightly misformatted, or don't match the stubs, leading to spurious and incorrect changes.
• The existing stubs are sometimes not sorted alphabetically. I'll fix this in a separate PR (Sort Python stubs consistently #1662), so that the diff of this PR will become more readable/meaningful.

With those things in mind, early feedback is welcome. I'm particularly interested in the opinion of @Hoikas, who has recently hand-written some stubs that will be overwritten by this script.

[dpogue]

The generated signature for PtLocalizedYesNoDialog is resulting in Python syntax errors (it has a / as an argument, which I think is supposed to have special meaning and not show up as an argument itself?)

[dgelessus]

I think / in parameter lists is allowed in real Python code since... some recent-ish version of Python 3. The actual syntax error is that the / appears after a *args (/ must come before *). This should get fixed along the way once I get type annotations working, because the manually type-annotated version of PtLocalizedYesNoDialog in the stub doesn't have this syntax error.

[dgelessus]

Type annotations are now supported by the stub generator. I've introduced a new Type: docstring prefix, which works similarly to the existing Params: prefix, but allows specifying a full function signature including a return type annotation (example: Type: (x: int, y: int) -> int) or the type of a property getter (example: Type: Tuple[str, int]).

I've also brought all of the C++-defined docstrings up-to-date with the manual changes and added type annotations in the stubs. This should resolve all of the spurious changes.

This PR is basically finished now. I'll un-draft it once #1662 is merged and I've rebased this PR onto that (so that this PR's diff is more readable for reviewing).