Handle generation numbers in BlobId#{to,from}GsUtilUri

[davidmandle]

Unlike gsutil, BlobId#toGsUtilUri currently ignores a BlobId's generation number, and BlobId#fromGsUtilUri doesn't parse generation numbers. It would be nice if, consistent with gsutil, fromGsUtilUri parsed any generation number in the URI so that references to particular versions of blobs could be made in URI format.

[jjathman]

I think this should have been noted as a potentially breaking change and likely created a new API for this usage. In our applications we had application A which is generating the GS URI using version 2.22.0 which now includes the generation in the URL. However, other applications are still using 2.11.x which incorrectly reads the new String.

[BenWhitehead]

Apologies for that @jjathman, I'll try and get a fix posted for the next release.