impl_serde_for_symbol! serializes as usize but deserializes as underlying type

[lemoncove]

I don't have a totally complete understanding of how all this works, so take all this with a grain of salt.

Here, impl_serde_for_symbol! serializes as usize...

string-interner/src/serde_impl.rs

Lines 91 to 96 in a8be633

	impl ::serde::Serialize for $crate::symbol::$name {
	fn serialize<T: ::serde::Serializer>(
	&self,
	serializer: T,
	) -> ::core::result::Result<T::Ok, T::Error> {
	self.to_usize().serialize(serializer)

...but then deserializes as $ty...

string-interner/src/serde_impl.rs

Lines 100 to 104 in a8be633

	impl<'de> ::serde::Deserialize<'de> for $crate::symbol::$name {
	fn deserialize<D: ::serde::Deserializer<'de>>(
	deserializer: D,
	) -> ::core::result::Result<Self, D::Error> {
	let index = <$ty as ::serde::Deserialize<'de>>::deserialize(deserializer)?;

...which, for SymbolU16 and SymbolU32 are u16 and u32. This is normally not a problem because in formats like JSON, a number is just a number. But when using binary-aware formats like bitcode, this results in a failure to deserialize unless using SymbolUsize, but of course a 64-bit integer is often going to be pretty overkill.

I think the solution is to deserialize as usize and then try Symbol::try_from_usize(). Not sure though.