Allows the return-type to be specified, allowing a concise final cast
after extracting the bit-type. Addresses the remaining `C4244` warnings
regarding `getBits`.
`constexpr` functions for extractint bitfields that lends itself a bit
better to emitting instructions like `bextr` on x86 or `ubfx` on arm64.
And may subjectively make things a bit more readable.
"Extract `5` bits" rather than `& 0x1F`.