LibLine: Parse CSI parameters and immediates

No behavior change, but it makes it easy to handle
page up and page down if we wanted to make them do something
in libline.

Libraries/LibLine/Editor.h

@@ -471,8 +471,9 @@ private:
     enum class InputState {
         Free,
         GotEscape,
-        GotEscapeFollowedByLeftBracket,
-        ExpectTerminator,
+        CSIExpectParameter,
+        CSIExpectIntermediate,
+        CSIExpectFinal,
     };
     InputState m_state { InputState::Free };