gettext.rs: allow translating non-literal strings

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.

fish-rust/src/wutil/gettext.rs

@@ -15,7 +15,7 @@ pub fn wgettext_impl_do_not_use_directly(text: &[wchar_t]) -> &'static wstr {
 /// Get a (possibly translated) string from a string literal.
 /// This returns a &'static wstr.
 macro_rules! wgettext {
-    ($string:literal) => {
+    ($string:expr) => {
         crate::wutil::gettext::wgettext_impl_do_not_use_directly(
             crate::wchar_ffi::u32cstr!($string).as_slice_with_nul(),
         )
@@ -27,7 +27,7 @@ macro_rules! wgettext {
 /// The result is a WString.
 macro_rules! wgettext_fmt {
     (
-    $string:literal, // format string
+    $string:expr, // format string
     $($args:expr),* // list of expressions
     $(,)?   // optional trailing comma
     ) => {