Use optimistic confirmation in getSignatureStatuses, and various downstream client methods (#14430)

* Add optimistically_confirmed field to TransactionStatus

* Update docs

* Convert new field to confirmation_status

* Update docs to confirmationStatus

* Update variants

* Update docs

* Just Confirmed

docs/src/developing/clients/jsonrpc-api.md

@@ -1945,6 +1945,7 @@ An array of:
   - `slot: <u64>` - The slot the transaction was processed
   - `confirmations: <usize | null>` - Number of blocks since signature confirmation, null if rooted, as well as finalized by a supermajority of the cluster
   - `err: <object | null>` - Error if transaction failed, null if transaction succeeded. [TransactionError definitions](https://github.com/solana-labs/solana/blob/master/sdk/src/transaction.rs#L24)
+  - `confirmationStatus: <string | null>` - The transaction's cluster confirmation status; either `processed`, `confirmed`, or `finalized`. See [Commitment](jsonrpc-api.md#configuring-state-commitment) for more on optimistic confirmation.
   - DEPRECATED: `status: <object>` - Transaction status
     - `"Ok": <null>` - Transaction was successful
     - `"Err": <ERR>` - Transaction failed with TransactionError
@@ -1983,7 +1984,8 @@ Result:
         "err": null,
         "status": {
           "Ok": null
-        }
+        },
+        "confirmationStatus": "confirmed",
       },
       null
     ]
@@ -2027,7 +2029,8 @@ Result:
         "err": null,
         "status": {
           "Ok": null
-        }
+        },
+        "confirmationStatus": "finalized",
       },
       null
     ]