Editor: multi cursor support

Adding a way to create multiple cursors that can insert/remove text at
arbitrary positions in the document. Adding cursors is done by pressing
alt + up/down or by clicking into the editor while holding the alt key.

Fixes: QTCREATORBUG-16013
Change-Id: I495d27d95a3d277220946616ef30efc241da0120
Reviewed-by: Christian Stenger <christian.stenger@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Artem Sokolovskii <artem.sokolovskii@qt.io>
Reviewed-by: David Schulz <david.schulz@qt.io>

src/libs/utils/uncommentselection.h

@@ -36,6 +36,8 @@ QT_END_NAMESPACE
 
 namespace Utils {
 
+class MultiTextCursor;
+
 class QTCREATOR_UTILS_EXPORT CommentDefinition
 {
 public:
@@ -62,4 +64,9 @@ QTextCursor unCommentSelection(const QTextCursor &cursor,
                                const CommentDefinition &definiton = CommentDefinition(),
                                bool preferSingleLine = false);
 
+QTCREATOR_UTILS_EXPORT
+MultiTextCursor unCommentSelection(const MultiTextCursor &cursor,
+                                   const CommentDefinition &definiton = CommentDefinition(),
+                                   bool preferSingleLine = false);
+
 } // namespace Utils