Gui: allow change ExpressionCompleter filter mode

Fixes #4428

Filter mode set to Qt::MatchContains for tree view search and link
property editor object search.

Other usage of the completer (e.g. property editor, speadsheet) defaults
to Qt::MatchContains, but can be changed using parameter,

    BaseApp/Preferences/Expression/CompleterMatchExact

src/Gui/DlgPropertyLink.cpp

@@ -76,6 +76,7 @@ DlgPropertyLink::DlgPropertyLink(QWidget* parent)
     ui->typeTree->hide();
     ui->searchBox->installEventFilter(this);
     ui->searchBox->setNoProperty(true);
+    ui->searchBox->setMatchExact(false);
 
     timer = new QTimer(this);
     timer->setSingleShot(true);