qedit: SampleGrabber pins should enumerate a preferred format only after the input pin is connected and a fully defined format is known.

qedit: In SampleGrabber ReceiveConnection check early the format type, return VFW_E_INVALIDMEDIATYPE like native.

We can't determine the correct block size until we read the header, and we
can't create the BigBlockFile until we know the correct block size. To
solve this dilemma, have StorageImpl calculate the file size it needs instead
of asking the BigBlockFile to "ensure a big block exists".

This should always be calculated based on the big block size.

Big block sizes can be 512 or 4096, so we define arrays that are large
enough in either case.