feat!: Spanner V2

[bshaffer]

TODO

• consider alternatives to withResultFunction(), such as MessageActiveRecordInterface::fromMessage(Message $message). which would allow the OperationResponse to call this method in order to "hydrate" the protobuf object
• investigate why info methods are now returning values for all fields
  • looked into this, it seems like V1 and V2 work the same, but the way the tests were written in V1, the response was mocked to not include all the fields.
• investigate project ID detection (it isn't working for V2 like it does for V1)
• Look into "Project ID Detection", which doesn't seem to be working well
• Investigate why multiplexedSessionPreviousTransactionId needed to be added to tests

TBD:

• can we remove the longRunningOperation methods on the handwritten classes in favor of using the existing list*Operations methods?
• What is the appropriate behavior when resumeOperation is called on a database for an instance operation?

[bshaffer]

closing in order to split this into two PRs.

See #7840 and #7841