Support a mix of edit and command in the code action response

[testforstephen]

The current ycmd implementation expects the code action response to have either edit or command, but not both. This is inconsistent with the LSP spec that allows both edit and command in the response. If both are supplied, the edit is applied first, then the command is executed. https://github.com/ycm-core/ycmd/blob/d3ae5557b65a56d7e8fa2cfcf8736d161af00db3/ycmd/completers/language_server/language_server_completer.py#L2687-L2700

[bstaletic]

How could I make jdt produce such a code action in order to test the implementation? I have tried a few things, but I could not trigger that assertion.