Add content description for weather complication.

This change sets the content description of the weather complication for
a11y, so that TalkBack reads both the weather condition (which is
presented as an icon visually), and the temperature.

Bug: 228406334
Fix: 228406334
Test: turn on TalkBack and verify weather complication reads both
weather condition and temperature
Test: atest DreamWeatherComplicationTest

Change-Id: I9d94b01776c59484eb5084e879634ac0742ae2bb