ust: Add swtbot for callstack view responsiveness

ust: Add swtbot for callstack view responsiveness

This swtbot test navigates a trace with the callstack view opened. This
test is not meant to be run in the performance test suite, but enabling
JUL logging with it allows to have a reproducible series of UI operations
and analyze its output.

Change-Id: If4081a4581bb1c774c3643fc0bb0dd418c421379
Signed-off-by: Geneviève Bastien <gbastien+lttng@versatic.net>
Reviewed-on: https://git.eclipse.org/r/80258
Reviewed-by: Hudson CI
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>