Optimize SegmentBlob#equals for segment blobs that originate from the same blob store

SegmentBlob#equals can be optimized for blobs originating from the same external blob store: In that case, SegmentBlob#getBlobId() can be used to determine if the blobs are equal or not. That change should avoid falling back to a byte-by-byte comparison if the two blobs have the same size, which can be very expensive for larger blobs.

The optimization should be placed behind a code/feature toggle or system property and disabled by default. The reason is that the contract of Blob#getContentIdentity does not mention the special case where Blobs reside in the same blob store.

As part of this story, integration and benchmark tests should be created to demonstrate gains in performance and correct behavior.