Documentation not working with R 4.1.1

[renkun-ken]

Looks like an upstream issue of repr:

[2021-08-12 13:16:43.195] internal error: Error: argument must be coercible to non-negative integer
Call: seq_len(head.end.idx)
Stack trace:
1: repr_help_files_with_topic_generic(obj, Rd2HTML)
2: repr_html.help_files_with_topic(hfile)
3: repr::repr_html(hfile)
4: workspace$get_help(token_result$token, token_result$package)
5: hover_reply(id, uri, self$workspace, document, point)
6: self$deliver(hover_reply(id, uri, self$workspace, document, point))
7: dispatch(self, id, params)

[2021-08-12 13:16:43.199] deliver:  ["Response", "Response", "Message", "R6"]

[Error - 1:16:43 PM] Request textDocument/hover failed.
  Message: Error: argument must be coercible to non-negative integer
Call: seq_len(head.end.idx)
Stack trace:
1: repr_help_files_with_topic_generic(obj, Rd2HTML)
2: repr_html.help_files_with_topic(hfile)
3: repr::repr_html(hfile)
4: workspace$get_help(token_result$token, token_result$package)
5: hover_reply(id, uri, self$workspace, document, point)
6: self$deliver(hover_reply(id, uri, self$workspace, document, point))
7: dispatch(self, id, params)

[renkun-ken]

I think we should use an internal get-help function instead of relying on repr since it is quite simple.