[iOS] - Add ability to set custom command-line switches

[Brandon-T]

Summary

• Add ability to set custom command-line switches/flags for Brave-Core

Resolves brave/brave-browser#39384

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. Enable the Debug menu in Settings
2. Scroll down to Brave Core Switches
3. Scroll down to "Add Custom Switch"
4. Enter Key: "env-ai-chat.bsg" and Value: "dev"
5. Save
6. Notice new switch added at the bottom of the screen with --env-ai-chat.bsg=dev as the sub-text.
7. Restart the app
8. Visit: brave://version and verify the command-line switch was added.
9. Swipe to delete the switch you added.
10. Verify that it was deleted in the UI.
11. Visit: brave://version and verify the command-line switch was removed.

Screenshots

[kylehickinson]

Prefer @Environment(\.dismiss) private var dismiss instead

[kylehickinson]

Probably shouldn't initialize State like this, best to pass in a regular var and onAppear set the State with that. If you're fine with the key passed in being ignored on subsequent body evaluations you can also make a explicit init method that sets the state like _key = State(initialValue: key) instead

[kylehickinson]

Prefer regular for loops

[stephendonner]

Verification PASSED using

Brave version 1.69 (57)
iOS 17.5.1 (21F90)
iPad Pro (12.9-inch) (2nd generation)

Steps:

1. installed 1.69 (57) via TestFlight
2. launched Brave
3. enabled the Debug menu in Settings
4. swiped down to BraveCore Switches
5. swiped down further to Add Custom Switch
6. tapped on it
7. input env-ai-chat.bsg for the key field
8. input dev for the value field
9. repeated for keys: env-leo and env-ai-chat-premium.bsg
10. did my usual purchase from account.bravesoftware.com of Leo Premium, using `issue39384@mailinator.com
11. restarted Brave
12. loaded an article on vox.com
13. tapped on Summarize this page
14. tapped on I understand

Confirmed it summarized correctly using Leo Premium credentials and Claude 3 Sonnet

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