Description:

Instead of adding all the transaction fields, have serialize only add the fields we need.

This lets developers use the code pattern:

```js
const txReq = await greeter.populateTransaction.setGreeting(greeting)
const tx = await signer.populateTransaction(txReq)
provider.estimateL1Gas(tx)
```

Instead of the more error prone:

```js
const txReq = await greeter.populateTransaction.setGreeting(greeting)
const tx = await signer.populateTransaction(txReq)
delete tx.from
delete tx.chainId
provider.estimateL1Gas(tx)
```