Finish modernizing convertFromHTMLToContentBlocks - max nesting bug fix

Summary:
The old convertFromHTMLToContentBlocks is capping depth to 4, v2 doesn't cap the depth.
DraftEditorContents-core component didn't handle cases of depth bigger then 4.
Similar to the current UI behavior, depth bigger then 4 will be shown as the same depth of 4.

Reviewed By: flarnie

Differential Revision: D7816688

fbshipit-source-id: 8989f0c5fb03bfcffc1e50575e35986d2491c3c2

src/component/contents/DraftEditorContents-core.react.js

@@ -58,7 +58,7 @@ const getListItemClasses = (
     'public/DraftStyleDefault/depth1': depth === 1,
     'public/DraftStyleDefault/depth2': depth === 2,
     'public/DraftStyleDefault/depth3': depth === 3,
-    'public/DraftStyleDefault/depth4': depth === 4,
+    'public/DraftStyleDefault/depth4': depth >= 4,
     'public/DraftStyleDefault/listLTR': direction === 'LTR',
     'public/DraftStyleDefault/listRTL': direction === 'RTL',
   });