Issue title: Symbols Max Items Computed doesn't work for 0
 Issue body: If `xml.symbols.maxItemsComputed` is set to 0, then all the symbols are still computed.
 Comments: 
 Comment 0: The default value the server uses if no settings are passed to it is 0. This means no symbols would be shown in the clients that don't send a default configuration to LemMinX. Is this a good default, or should I make 5000 the default on the server side?
{'source': 'GithubIssues', 'repo_name_with_owner': 'eclipse/lemminx', 'issue_id': 712877930, 'repo_stars': 115.0}