Copy more doc comments to JS/TS files, unescape comments (#2070)

* Copy more doc comments to JS/TS files, unescape comments

* Move unescape code to macro-support

crates/backend/src/ast.rs

@@ -264,6 +264,7 @@ pub struct Enum {
 pub struct Variant {
     pub name: Ident,
     pub value: u32,
+    pub comments: Vec<String>,
 }
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]

crates/backend/src/encode.rs

@@ -227,6 +227,7 @@ fn shared_variant<'a>(v: &'a ast::Variant, intern: &'a Interner) -> EnumVariant<
     EnumVariant {
         name: intern.intern(&v.name),
         value: v.value,
+        comments: v.comments.iter().map(|s| &**s).collect(),
     }
 }