Global flag to prefer 32bit whenever possible

[mnielsm]

Because of speed and because I don't need the 64bit accuracy I declare allconstants with numba.types.float32 and numba.types.int32 but this is quite cumbersome if i need to do it everywhere

Would it be possible to add a global flag to request numba to declare constants as 32bit by default instead of 64bit and to prefer 32bit functions as much as possible.

[gmarkall]

Related: #7613

[gmarkall]

Work on alternative typing systems also being done in #9513 and #9548.

[dlee992]

also tag with #9409 meta issue.