graphql-syntax: add comments explaining FloatNode

Summary: It was a bit confusing why we had certain fields in FloatNode. This change adds some comments to help future readers understand.

Reviewed By: captbaritone

Differential Revision: D48117872

fbshipit-source-id: ea7bad15b47761807887c77484ab01f40102f422

compiler/crates/graphql-syntax/src/node/constant_value.rs

@@ -120,9 +120,10 @@ impl fmt::Display for IntNode {
 #[derive(Clone, Debug, Eq, PartialEq, Ord, PartialOrd, Hash)]
 pub struct FloatNode {
     pub token: Token,
+    /// NOTE: we can't just store an f64 here because it doesn't implement Hash, Eq, Ord
     pub value: FloatValue,
     /// Preserve a value, as it was represented in the source
-    /// TODO: We may remove this, as we migrate from JS
+    /// NOTE: this is needed for pretty-printing the AST to ensure we don't change what was in the source
     pub source_value: StringKey,
 }