docparser: Improve trait/mixin handling
docparser: Improve trait/mixin handling

JS mixins and PHP traits are now considered the same thing.

Change-Id: I71eb9499781cc1d8e30e017ae72bab087a125e2f

wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui