Adds the performance harness, state-verification suites, gallery
showcases and reference docs accumulated for the 6.0 release, plus
control-level fixes:
- tools/performances/AtomUI.Performance + AtomUI.GalleryPerformance
scaffolding with per-control scenarios and verification suites
- docs/performances/** baselines and plans
- controlgallery/** showcase data refreshes (icon gallery, range time
pickers, multi-select cascader strategies, etc.)
- ListBox: re-apply filter on OnLoaded when FilterValue is preset
- SelectCandidateList: visible-item selection mapping under filter
- RangeDatePicker: floating popup arrow even with IsShowTime=true
chinboy