Undocumented method for "slice" class

Documentation

The "slice" class has a method "indices" that, when given a length of a sequence, will return a tuple with (start, stop, step) that is adjusted for the length of that sequence. This method is completely undocumented

For example,

x=slice(0, 10, -2)
x.indices(5) #This returns (0, 4, -2)
x.indices(10) #This returns (0, 9, -2)
x.indices(100) #This returns (0, 9, -2)

The only example that I could find in any official Python documents is this, there is a single reference to this method at the bottom of the page. However, as of the lastest version of Python, which is 3.11.0 at the time of writing, using this method in a standard installation of CPython still works.

• PR: gh-99129

Start at the Python documentation page for the slice class linked in the issue and inspect how its methods are documented. Add documentation for slice.indices(), including its length argument, returned tuple, and behavior examples; done means the method is described alongside the class and the examples are accurate.