[log] Extract the popup text field used for user completion

Will be used for 'jump to commit'
[log] "Go To Commit" action

* Provide all references to the text field completion.
* Delegate all work to the VcsLog interface.
* If reference was specified, jump to its hash.
* Otherwise try to jump to the hash: delegate to VcsLogUi and further
  to DataPack to get the Node of Hash starting from the given string.
* If full log is not loaded and we haven't found anything,
  request to load full log and try again.

  As opposed to jumpToHash with the given Hash, we can't assume that
  the given String represents a valid Hash which exists in this
  repository => we must check if full log is already showing to
  prevent infinite request.
[log] IDEA-115980 Don't show Git actions if there are no Git roots