Progresses #8668, #7864, #10041

For the last two, #7864 and #10041 -- more work is needed to completely resolve this but @BboyAkers has inflight work that will help. This PR doesn't change how we are generating custom block explorer URLs.

Relies on MetaMask/etherscan-link#32

Details:

• adds new utility method for building a blockExplorerUrl that prefers the chainId parameter of a transaction, but falls back to metamaskNetworkId
• Remove a now unused older version that only used metamaskNetworkId
• Use the new utility method in all places where building a link for a transaction
• In the swaps page networkId/rpcPrefs were being pulled from redux using useSelector but then were only being passed into AwaitingSwap. Moved those selectors directly into AwaitingSwap
• After confirming that the aforementioned state items were only used as part of building a blockExplorerUrl, removed networkId in favor of chainId.
• Noticed that when building activity entries for a transaction's detail view, the activity entry copies the hash of the current transaction into each activity object. Later, in the click handler for clicking on an activity entry, the hash of the activity object is used along with the metamaskNetworkId of the primaryTransaction. I realize it is unlikely, perhaps impossible, for the metamaskNetworkId to differ from one transaction in a group to another but it caused me some confusion so I opted to clean this up and add metamaskNetworkId and chainId to the activity object.
• grabs rpcPrefs for current network and sends them to showTransactionNotification so that we can link custom network notifications properly.
• adds rpcPrefs in activity list so that proper URL generation can occur