LibJS: Convert resolve_binding() to ThrowCompletionOr

The spec has a note stating that resolve binding will always return a
reference whose [[ReferencedName]] field is name. However this is not
correct as the underlying method GetIdentifierReference may throw on
env.HasBinding(name) thus it can throw. However, there are some
scenarios where it cannot throw because the reference is known to exist
in that case we use MUST with a comment.

Userland/Libraries/LibJS/Runtime/AbstractOperations.cpp

@@ -215,7 +215,8 @@ ThrowCompletionOr<void> initialize_bound_name(GlobalObject& global_object, FlySt
     // 2. Else,
     else {
         // a. Let lhs be ResolveBinding(name).
-        auto lhs = vm.resolve_binding(name);
+        // NOTE: Although the spec pretends resolve_binding cannot fail it can just not in this case.
+        auto lhs = MUST(vm.resolve_binding(name));
 
         // b. Return ? PutValue(lhs, value).
         return TRY(lhs.put_value(global_object, value));