Rename Rect2 and Rect2i clip() to intersection()

[madmiraal]

As originally identified here, Rect2 and Rect2i's method clip() is the same as 3D's AABB's method intersection(). These methods should have the same name. This PR renames Rect2 and Rect2i's method clip() to intersection(), because, although the method can be used to clip a rectangle, it doesn't clip the current rectangle. Instead, it returns the intersection between this rectangle and another rectangle. Even the current documentation describes it as such:

Returns the intersection of this Rect2 and b.

Part of #16863.

[akien-mga]

Thanks!

[aaronfranke]

Should also be done for C#.

EDIT: #44582