Translate LongLong types to f64

Any LongLong still present after flattening now gets translated to a `f64` type
so we can bind these types. While not a true integral value or truely 64-bits of
integer precision, it's all JS has anyway!

crates/backend/src/codegen.rs

@@ -1087,7 +1087,7 @@ impl ToTokens for ast::Const {
             Null => unimplemented!(),
         };
 
-        let declaration = quote!(#vis const #name: #ty = #value;);
+        let declaration = quote!(#vis const #name: #ty = #value as #ty;);
 
         if let Some(class) = &self.class {
             (quote! {