This PR fixes many issues with our typestubs, and also adds amypy.stubtest test program on CI to test for issues in typestubs.

Firstly this PR moves typestubs frombuildconfig/pygame-stubs tobuildconfig/stubs/pygame because stubtest needs to run in a directory where pygame stubs are inpygame subdir.

Some of our util typestubs in_common has a leading underscore, which leads to pycharm not recognising those (I heard from someone, I did not test this myself), so I fixed this, and it still works withmypy after the changes

I added some missing stubs, some in_sdl2 and also stubs forbase andrwobject.

Another change I did was to properly typeVectorElementwiseProxy as a generic, so now it works well with bothVector2 andVector3 types, and correctly errors at incorrectelementwise() calls (like mixing vector2 and vector3 elementwise)

Apart from that, there are a lot more fixes in this PR, so I believe this PR fixes most of the typestub issues, but there might still be issues left, that are not caught by mypy stubtest. A good future enhancement would be running typestub tests on our examples and maybe some dedicated unit tests for this, but this PR is already too large, so this is something for later.

I've tried to keep code changes to a minimum in this PR, but there are a few places where I had to make some code changes, for instance, I replacedclock_init withclock_new following the PR#3001 becauseClock.__init__ leads to some stub issues, and also according to python docs fortp_new

A good rule of thumb is that for immutable types, all initialization should take place intp_new, while for mutable types, most initialization should be deferred totp_init.

So clock being immutable, this change makes sense