TMF: Fix performance issue in the filter dialog of the time graph view

TMF: Fix performance issue in the filter dialog of the time graph view

This patch improves the performance of opening the filter dialog
of the time graph view. The dialog can take many minutes to open
with traces that contain 10 000+ threads, because of an O(n²)
algorithm to associate threads with their parent. With this change,
it takes about 8 seconds to open the dialog.

Change-Id: Ib4f4c41583705041a3df9d7ca26d2f883ffd9a43
Signed-off-by: Mathieu Cote <mathieu.cote@polymtl.ca>
Reviewed-on: https://git.eclipse.org/r/41789
Reviewed-by: Genevieve Bastien <gbastien+lttng@versatic.net>
Tested-by: Genevieve Bastien <gbastien+lttng@versatic.net>
Reviewed-by: Hudson CI
Reviewed-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
Tested-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>