Supplements Missing Functionalities for FileOpenPicker.FileTypeFilter and FileSavePicker.FilterTypeChoices

[DinahK-2SO]

Description

This PR addresses the following missing functionalities for FileOpenPicker.FileTypeFilter and FileSavePicker.FilterTypeChoices:

FileOpenPicker.FileTypeFilter

Test code (C++):

winrt::Microsoft::Windows::Storage::Pickers::FileOpenPicker picker{ AppWindow().Id() };
picker.FileTypeFilter().Append(L".jpg");
picker.FileTypeFilter().Append(L".png");
auto& file = co_await picker.PickSingleFileAsync();

1. When FileTypeFilters are defined, append a file type filter that includes all the already defined file types.
   With this PR:
   
   Without this PR:
   

FileSavePicker.FilterTypeChoices

Test code (C++):

winrt::Microsoft::Windows::Storage::Pickers::FileSavePicker picker{ AppWindow().Id() };
picker.FileTypeChoices().Insert(L"Documents", single_threaded_vector<hstring>({ L".txt", L".doc", L".docx", L".pdf"}));
picker.FileTypeChoices().Insert(L"Pictures", single_threaded_vector<hstring>({ L".jpg", L"jpeg", L".png", L".bmp"}));
auto& file = co_await picker.PickSaveFileAsync();

1. When FileTypeChoices are defined and a file is saved with an unknown extension, automatically append the first extension from the choices (utilizing the built-in protection mechanisms of the COM file dialog).
   With this PR:
   
   Without this PR:
   

2. When multiple categories are defined in FileTypeChoices, the suggested file extension should change according to the selected category.
   With this PR:
   
   Without this PR:
   

[ghost1372]

@DinahK-2SO
Wouldn't it be better if the All Files option was the first option? Currently, All Files is the last option.(I mean it should be placed before all types, not after them.)