feat(wallet): Network selection during onboarding on iOS

[StephenHeaps]

Resolves brave/brave-browser#37740

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. In Wallet onboarding, tap Need a new wallet? to create a new wallet
2. After the legal step, verify you are shown a grid of available networks
3. Verify you can select / de-select networks (except for Ethereum Mainnet & Solana Mainnet)
4. Toggle Show Testnets
5. Verify testnets are shown at bottom of the networks grid
6. After onboarding, verify an account is created for each network selected during onboarding
   • For Filecoin Testnet and/or Bitcoin Testnet, this should be a separate account for Testnet than the Mainnet account(s)
7. Open Web3 Settings and tap Networks
8. Verify the networks selected during onboarding are visible (eye icon)
9. Verify the networks not selected during onboarding are not visible (crossed out eye icon)
10. Reset your wallet
11. In Wallet onboarding, tap Already have a wallet? to restore an existing wallet.
12. After the legal step, verify you are shown a grid of available networks
13. Verify you can select / de-select networks (except for Ethereum Mainnet & Solana Mainnet)
14. Toggle Show Testnets
15. Verify testnets are shown at bottom of the networks grid
16. Verify the networks selected during onboarding are visible (eye icon)
17. Verify the networks not selected during onboarding are not visible (crossed out eye icon)

[brave-builds]

A Storybook has been deployed to preview UI for the latest push

[github-actions]

Chromium major version is behind target branch (139.0.7258.127 vs 140.0.7339.16). Please rebase.

[github-actions]

Chromium major version is behind target branch (140.0.7339.133 vs 141.0.7390.30). Please rebase.