A following commit will pass global string constants to the gettext macro.
This is not ideal because we might accidentally use the constants without
gettext (which we should never do). To fix that we might need to define a
macro per constant, or use a proc macro which is maybe not worth it.
This adds an implementation of fish_wcstoi in Rust, mirroring the one in
fish. As Rust does not have a string to number which infers the radix
(i.e. looks for leading 0x or 0), we add that manually.
