[PATCH] dwrite: Add IDWriteFontFace5::Equals() stub.

[Nikolay Sivov]

Sorry about that.

Since we don't support variations at the moment, it'd be good enough to
duplicate what dwritefont3_Equals() does, by comparing <index,
simulations, file>. It's fine to use unsafe_impl(other) and assume that
there is always 1 file. Loop for file_count works too if you prefer, but
formats like Type 1 that use multiple files are not meant to work.