PathChooser: Allow for chooser-only selection of files/directories

Makes the line edit disabled and read-only in that case.
We also need to change the custom context menu from the line edit to the
path chooser itself, because disabled widgets do not show a context
menu, but we still want to see the select & copy, and the special
items for opening explorer or terminal.

Task-number: QTCREATORBUG-23798
Change-Id: Ib653b4eaaedfbe54c614377795ddc52d21ac12c0
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

src/libs/utils/pathchooser.h

@@ -138,6 +138,9 @@ public:
     bool isReadOnly() const;
     void setReadOnly(bool b);
 
+    bool isFileDialogOnly() const;
+    void setFileDialogOnly(bool b);
+
     void triggerChanged();
 
     // global handler for adding context menus to ALL pathchooser
@@ -156,6 +159,7 @@ private:
     QString makeDialogTitle(const QString &title);
     void slotBrowse();
     void contextMenuRequested(const QPoint &pos);
+    void updateReadOnlyStateOfSubwidgets();
 
 signals:
     void validChanged(bool validState);