DiscIO: Replace IsDataSizeAccurate with GetDataSizeType

Previously, we had WBFS and CISO which both returned an upper bound
of the size, and other formats which returned an accurate size. But
now we also have NFS, which returns a lower bound of the size. To
allow VolumeVerifier to make better informed decisions for NFS, let's
use an enum instead of a bool for the type of data size a blob has.

Source/Core/DiscIO/WIABlob.cpp

@@ -1731,7 +1731,7 @@ WIARVZFileReader<RVZ>::Convert(BlobReader* infile, const VolumeDisc* infile_volu
                                File::IOFile* outfile, WIARVZCompressionType compression_type,
                                int compression_level, int chunk_size, CompressCB callback)
 {
-  ASSERT(infile->IsDataSizeAccurate());
+  ASSERT(infile->GetDataSizeType() == DataSizeType::Accurate);
   ASSERT(chunk_size > 0);
 
   const u64 iso_size = infile->GetDataSize();