[buffer-diff] Fix check for glyph flag equality I'm not sure if the old behavior was intentional, but it was checking that the glyph flags were a subset of the reference buffer's glyph flags. I don't see why that is useful. Fix that. Then make the buffer-verify code ignore flag differences when verifying buffers, since our unsafe-to-concat flag at least, is conservative and not guaranteed to be produced the same in fragments. See: https://github.com/harfbuzz/harfbuzz/issues/3888