Support `^` for StaticInt?

[ojwoodford]

Currently, the following code throws an error:

using Static
static(2) ^ static(3)

The desired/expected output is static(8). Likewise, 2 ^ static(3) and static(2) ^ 3 should both return 8::Int.

Is there any reason not to support ^ for StaticInt? If not, shall I create a PR to add it?

[Tokazama]

Only reason not to do it is if it causes a bunch of invalidations. Should be a simple PR to check though