fix: make password visibility toggle buttons accessible

[avinxshKD]

Fixes #3850

Changes

• LoginForm: password visibility toggle now has accessible label that toggles between "Show password as plain text" and "Hide password"
• SignupForm: both password and confirm password toggles now have accessible labels
• Added translation keys for toggle button labels in en-US locale

I have verified that this pull request:

• has no linting errors (npm run lint)
• has no test errors (npm run test)
• has no typecheck errors (npm run typecheck)
• is from a uniquely-named feature branch and is up to date with the develop branch
• is descriptively named and links to an issue number, i.e. Fixes #3850
• meets the standards outlined in the accessibility guidelines

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[avinxshKD]

@raclim hey worked on the fix, pls let me know if any adjustments needed, Happy to.

[avinxshKD]

Hey @raclim the new aria-label on the toggle button caused getByLabelText(/password/i) to match two elements. Anchored it to /^password$/i to target only the input.

[raclim]

Thanks for fixing it so quickly! Just want to note that for future PRs, running through the checklist in the PR template before submitting can help catch these errors sooner!