internal/web3ext: Add eth.getProof

[ryanschneider]

I wanted to give eth_getProof a test drive but found that it wasn't available in the console provided by geth attach so added it to web3ext. It's not 100% clear to me when I should add methods to web3ext vs. internal/jsre/deps/web3.js (followed by a go generate), so I'm happy to change this PR to do the changes in web3.js instead if preferred.

Both ways give me the same result (I elided the proof values below with "..." to keep this PR text from being too long, in the actual output the correct hex strings are output.

> eth.getProof("0x09d8b66c48424324b25754a873e290cae5dca439", ["0x0"], "latest")
{
  accountProof: ["...", "...", "...", "...", "...", "...", "...", "..."],
  address: "0x09d8b66c48424324b25754a873e290cae5dca439",
  balance: "0x0",
  codeHash: "0x49a2e4941f66f56811a3ba9153696e692b305bc57c3b4e0a727b8c0c422f275f",
  nonce: "0x1",
  storageHash: "0x8c07d8edd90c3adf163ddcd046e482b1b061fac7fb31e10306aedc8f1d84f26f",
  storageProof: [{
      key: "0x0",
      proof: ["...", "...", "...", "..."],
      value: "0xdff10fcaccc3b18a1604509e9b4d0b9a7091278"
  }]
}

[ryanschneider]

Pinging @holiman and @ligi since you both approved the related PR #17737 and no reviewer for this area is specified in CODEOWNERS.

[holiman]

It's not 100% clear to me when I should add methods to web3ext vs. internal/jsre/deps/web3.js

... me neither 🤷‍♂️ ...

[fjl]

We don't want to modify web3.js directly, adding it to the extension file is fine.