[Accessibility] In QWindowsUIAMainProvider - StaticText controls should not return a ValueProvider

On Windows, Narrator reads out static texts and announces whether they are editable or not, which is confusing to users. It should only read out the text.

This is because all controls implement the Value pattern, which makes Narrator call the get_IsReadOnly method and announce "editable text" or "read only" based on what the result is.