Debugger tooltips issues

There are some issues with debugger tooltips:
1) Tooltips for global variables (primitive types) appear only once.
2) Tooltips for global structures are not expandable (QTCREATORBUG-19574).
3) After restart debugger, tooltips for global variables do not work at all,
and there is an issue with expanding local structures.

I found the way to resolve all these issues, but I'm not sure this way is proper.
Gerrit: https://codereview.qt-project.org/c/qt-creator/qt-creator/+/296043
Tested only with GDB Engine.