Revert incorrect <flat_set> change, and update test failure reason - #5522

Revert incorrect <flat_set> change, and update test failure reason#5522

Stephan T. Lavavej (StephanTLavavej) merged 4 commits into

microsoft:feature/flat_mapmicrosoft/STL:feature/flat_mapfrom

AlexGuteniev:flat_set_strongAlexGuteniev/STL:flat_set_strongCopy head branch name to clipboard