Use synchronous APIs for AppExtensionCatalog

[lhecker]

MSFT-43215694 added IAppExtensionCatalog2::FindAll and IAppExtension3::GetPublicFolder. If they release publicly, we should use those in the settings model because extractValueFromTaskWithoutMainThreadAwait is slow, wrong and ✨pain✨ (just that one call to FindAllAsync + await is like 4% of the total startup cost). I personally wouldn't even keep the old code because of that.

[zadjii-msft]

xlink #6726 is also something we need to fix in the next version of the SDK