update for primitives (#6819)

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Fixes #6774

Preview:
https://dart-dev--pr6819-js-types-1vzi950e.web.app/interop/js-interop/js-types

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Author: connie-ooi

src/content/interop/js-interop/js-types.md

@@ -28,9 +28,7 @@ In order to interact with and examine these JS values, you should use
 JS types form a natural type hierarchy:
 
 - Top type: `JSAny`, which is any non-nullish JS value
-  - Primitives: `JSNumber`, `JSBoolean`, `JSString`
-  - `JSSymbol`
-  - `JSBigInt`
+  - Primitives: `JSNumber`, `JSBoolean`, `JSString`, `JSSymbol`, `JSBigInt`
   - `JSObject`, which is any JS object
     - `JSFunction`
       - `JSExportedDartFunction`, which represents a Dart callback that was