Debugger: Fix async tooltip handling

For now, only the gdb engine can handle complex tooltips
requiring async re-evaluation, cdb and lldb will show
and expand only items that are available in the Locals view.

This patch disables also the save/restore feature for
pinned tooltips.

Task-number: QTCREATORBUG-13255
Task-number: QTCREATORBUG-13052
Change-Id: Ic25616fede0f5c4343a92b631f01e60bfc5e9d81
Reviewed-by: David Schulz <david.schulz@theqtcompany.com>
Reviewed-by: Christian Stenger <christian.stenger@theqtcompany.com>