Replace occurrences of "Windows 8.x Store"

Related to https://github.com/dotnet/dotnet-api-docs/pull/7376

Some API docs mention Windows 8.x Store, but the majority of occurrences does not have anything specific to Windows 8 or Windows Store. For example:

1\. Async IO API remarks have text like this: https://docs.microsoft.com/en-us/dotnet/api/system.io.stream.copytoasync?view=net-6.0

>This performance consideration is particularly important in a Windows 8.x Store app or desktop app where a time-consuming stream operation can block the UI thread and make your app appear as if it is not working.

This is actually talking about any GUI apps. I think we can mass-replace these as in linked PR to

>This performance consideration is particularly important in applications where a time-consuming stream operation can block the UI thread and make your app appear as if it is not working.

2\. Some APIs have WinRT-specific info like this: https://docs.microsoft.com/en-us/dotnet/api/system.io.isolatedstorage.isolatedstorage?view=net-6.0

> Isolated storage is not available for Windows 8.x Store apps.

This is relevant for WinRT/UWP, but not only in Windows 8. In this case we need to find a suitable replacement term, probably "Windows Runtime apps" or "Universal Windows apps".