Add types for tkinter.Canvas.canvasx and tkinter.Canvas.canvasy

[Akuli]

Example:

>>> import tkinter
>>> c = tkinter.Canvas()
>>> c.canvasx(5.1, gridspacing=3.03)
6.06
>>> c.canvasx('5m', gridspacing='1m')
18.91891891891892

[github-actions]

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