linux.ui: add a centralized registry of event styles.

linux.ui: add a centralized registry of event styles.

This ensures that a state in the Control Flow view and the Resources
view will always be the same color. Also allows localizable help text.

Change-Id: I17cf2ad0e3bda0e254a1ee6d12df0aa96177647a
Signed-off-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/85091
Reviewed-by: Hudson CI
Reviewed-by: Genevieve Bastien <gbastien+lttng@versatic.net>
Tested-by: Genevieve Bastien <gbastien+lttng@versatic.net>