Unable to use the XTree finder along with multiselect

The current implementation of the XTree finder plugin disables every selected item in a tree when performing a search (see https://github.com/xwiki/xwiki-platform/blob/master/xwiki-platform-core/xwiki-platform-tree/xwiki-platform-tree-webjar/src/main/webjar/finder.js#L46).

This can become a problem when using the finder plugin along with the multiselect plugin.

Possible solution : create a configuration option to determine if the selected tree items should be cleared when performing a search.