feat(wallet): Add contract address link out to transaction confirmation panel

[StephenHeaps]

Resolves brave/brave-browser#39720

Submitter Checklist:

• I confirm that no security/privacy review is needed and no other type of reviews are needed, or that I have requested them
• There is a ticket for my issue
• Used Github auto-closing keywords in the PR description above
• Wrote a good PR/commit description
• Squashed any review feedback or "fixup" commits before merge, so that history is a record of what happened in the repo, not your PR
• Added appropriate labels (QA/Yes or QA/No; release-notes/include or release-notes/exclude; OS/...) to the associated issue
• Checked the PR locally:
  • npm run test -- brave_browser_tests, npm run test -- brave_unit_tests wiki
  • npm run presubmit wiki, npm run gn_check, npm run tslint
• Ran git rebase master (if needed)

Reviewer Checklist:

• A security review is not needed, or a link to one is included in the PR description
• New files have MPL-2.0 license header
• Adequate test coverage exists to prevent regressions
• Major classes, functions and non-trivial code blocks are well-commented
• Changes in component dependencies are properly reflected in gn
• Code follows the style guide
• Test plan is specified in PR before merging

After-merge Checklist:

• The associated issue milestone is set to the smallest version that the
  changes has landed on
• All relevant documentation has been updated, for instance:
  • https://github.com/brave/brave-browser/wiki/Deviations-from-Chromium-(features-we-disable-or-remove)
  • https://github.com/brave/brave-browser/wiki/Proxy-redirected-URLs
  • https://github.com/brave/brave-browser/wiki/Fingerprinting-Protections
  • https://github.com/brave/brave-browser/wiki/Brave%E2%80%99s-Use-of-Referral-Codes
  • https://github.com/brave/brave-browser/wiki/Web-Compatibility-Exceptions-in-Brave
  • https://github.com/brave/brave-browser/wiki/QA-Guide
  • https://github.com/brave/brave-browser/wiki/P3A

Test Plan:

1. Visit https://bbondy.github.io/eth-manual-tests/request.html
2. Tap eth_requestAccounts and connect an ethereum account
3. In the wallet panel, change the network to Sepolia Test Network
4. Enter a to address next to eth_signTransaction then tap eth_signTransaction
5. Verify the to address is still displayed as before (truncated address if it's not one from your wallet, otherwise will show account name)
6. Enter 0xdb6f1920a889355780af7570773609bd8cb1f498 next to eth_signTransaction then tap eth_signTransaction
   • This is the contract address for ExchangeProxyFlashWallet from ZeroEx: https://0x.org/docs/developer-resources/contract-addresses
7. Verify that the to address displays as Contract Address with a link out button, and tapping on the contract address will link out to the block explorer showing the code for the contract address.