Re: cocos-creator/3d-tasks#
Changelog:
1. Fix the value of windowHeight and windowWidth pixelRatio return by getSystemInfo(Sync) on VIVO platform
Add ral/API.md as ral API reference
2. Add API getFeaturePropertyInt which was described in ral/API.md
3. Fix CP call sys.garbageCollect() will get TypeError on OVH and cocosplay