Bundle stdlib runtime for playground (rescript-lang#7255)

* bundle stdlib JS files for playground

* stop uncapitalizing js files in playground imports

Author: tsnobip

compiler/core/js_name_of_module_id.ml

@@ -31,7 +31,7 @@ let string_of_module_id_in_browser (x : Lam_module_ident.t) =
   match x.kind with
   | External {name} -> name
   | Runtime | Ml -> 
-    "./stdlib/" ^  Ext_string.uncapitalize_ascii x.id.name ^ ".js"
+    "./stdlib/" ^ x.id.name ^ ".js"
 
 let string_of_module_id 
     (id : Lam_module_ident.t)