Add starts_with and ends_with to hstring

[jaigak]

C++ 20's basic_string has starts_with and ends_with and since hstring's API is designed to look like a wstring, hstring should have these methods

[jaigak]

Seems like wstring actually creates a std::wstring_view and calls it's ends_with and starts_with method respectively

[sylveon]

You can do similar with an hstring:

winrt::hstring str;

if (std::wstring_view(str).starts_with(L"foo"))
{
    // Code
}

[kennykerr]

Feel free to contribute these additions - they can be quite handy.