internal/ethapi/api: return maxFeePerGas for gasPrice for EIP-1559 txs

[lightclient]

Currently geth returns 0 null(console converts to 0) for gasPrice for pending transactions:

> params = { from: me, to: me, maxFeePerGas: "0x1000000000", maxTipPerGas: "0x0", gas: "0x5208" }
{
  from: "0xc0ffee61108b46c8b84c63df14e3a607ac981e93",
  gas: "0x5208",
  maxFeePerGas: "0x1000000000",
  maxTipPerGas: "0x0",
  to: "0xc0ffee61108b46c8b84c63df14e3a607ac981e93"
}
> personal.sendTransaction(params)
"0xd7291f16ce57eb4e6aaae4b3d81f3f16ed947763cbed230eef3d9d1cb395fa5d"
> eth.getTransaction("0xd7291f16ce57eb4e6aaae4b3d81f3f16ed947763cbed230eef3d9d1cb395fa5d")
{
  accessList: [],
  blockHash: null,
  blockNumber: null,
  chainId: "0x5",
  from: "0xc0ffee61108b46c8b84c63df14e3a607ac981e93",
  gas: 21000,
  gasPrice: 0,
  hash: "0xd7291f16ce57eb4e6aaae4b3d81f3f16ed947763cbed230eef3d9d1cb395fa5d",
  input: "0x",
  maxFeePerGas: "0x1000000000",
  maxPriorityFeePerGas: "0x12a05f1f9",
  nonce: 0,
  r: "0x10f320d15d1d8c84ae687c9f446379d5c4c76e16146361349002e0af77996fc0",
  s: "0x23c3e3bf21d272a1978f8923603171e462740764f5e03c1ef859f318fc72b34d",
  to: "0xc0ffee61108b46c8b84c63df14e3a607ac981e93",
  transactionIndex: null,
  type: "0x2",
  v: "0x1",
  value: 0
}

After this change, it will return maxFeePerGas as specified by the RPC spec:

> params = { from: me, to: me, maxFeePerGas: "0x1000000000", maxTipPerGas: "0x0", gas: "0x5208" }
{
  from: "0xc0ffee61108b46c8b84c63df14e3a607ac981e93",
  gas: "0x5208",
  maxFeePerGas: "0x1000000000",
  maxTipPerGas: "0x0",
  to: "0xc0ffee61108b46c8b84c63df14e3a607ac981e93"
}
> personal.sendTransaction(params)
"0x646d8b7343e06c3f944c022c7f2c898a7ff8a84c714f967bd75f60d3ca04710b"
> eth.getTransaction("0x646d8b7343e06c3f944c022c7f2c898a7ff8a84c714f967bd75f60d3ca04710b")
{
  accessList: [],
  blockHash: null,
  blockNumber: null,
  chainId: "0x5",
  from: "0xc0ffee61108b46c8b84c63df14e3a607ac981e93",
  gas: 21000,
  gasPrice: 68719476736,
  hash: "0x646d8b7343e06c3f944c022c7f2c898a7ff8a84c714f967bd75f60d3ca04710b",
  input: "0x",
  maxFeePerGas: "0x1000000000",
  maxPriorityFeePerGas: "0x12a05f1f9",
  nonce: 1,
  r: "0xf755782c9d7455ce2ffddafbb974faabc24801062d86ff471b3d7a132c3bb88d",
  s: "0x28fee09dc49d86c0214ee7c95cce30fd658494ee5810ccfe2649fbd3035ae370",
  to: "0xc0ffee61108b46c8b84c63df14e3a607ac981e93",
  transactionIndex: null,
  type: "0x2",
  v: "0x1",
  value: 0
}

edit: I realize I included an invalid value maxTipPerGas, but it ended up just estimating a priority fee so I don't think it affects the overall issue at all.

[lightclient]

Turns out, gasPrice is actually null. The console just coerced it into 0.

$ curl http://localhost:8645 -H 'Content-Type: application/json' -d '{"method":"eth_getTransactionByHash","id":1,"jsonrpc":"2.0", "params":["0xad8ca38344e48648b322d87c64ae4c4e3d9a8c055069abe507cf1d43d3d5bdc1"]}'

{"jsonrpc":"2.0","id":1,"result":{"blockHash":null,"blockNumber":null,"from":"0xc0ffee61108b46c8b84c63df14e3a607ac981e93","gas":"0x5208","gasPrice":null,"maxFeePerGas":"0x1000000000","maxPriorityFeePerGas":"0x0","hash":"0xad8ca38344e48648b322d87c64ae4c4e3d9a8c055069abe507cf1d43d3d5bdc1","input":"0x","nonce":"0x2","to":"0xc0ffee61108b46c8b84c63df14e3a607ac981e93","transactionIndex":null,"value":"0x0","type":"0x2","accessList":[],"chainId":"0x5","v":"0x1","r":"0x8d404089a6a6394f4095b33faac73e7cc32b23527c35a976a56b56fca29d6eeb","s":"0x4d26600698e6c81e3e9f2dcc4645d9b142b42328eec4ee50b411c6ac00b18d8d"}}