feedback-vibra: Add support for patterns

Add a new class that takes an array of durations and magnitudes.
A magnitude of 0 indicates a pause.

We can consider dropping the VibraRumble class at some point as that
is a special case of VibraPeriodic now however as the feedbacks are
encoded in the themes let's make sure VibraPattern is good API before
deprecating VibraRumble.

Signed-off-by: Guido Günther <agx@sigxcpu.org>

src/fbd-feedback-vibra-rumble.c

@@ -18,6 +18,8 @@
  * The #FbdVibraVibraRumble describes the properties of a haptic feedback
  * event. It knows nothing about the hardware itself but calls
  * #FbdDevVibra for that.
+ *
+ * TODO: could be dropped in favor of the more flexible `FbdFeedbackVibraPattern`.
  */
 
 enum {