[PM-13876] improve credential generator options validation

[audreyality]

🎟️ Tracking

https://bitwarden.atlassian.net/browse/PM-13876

📔 Objective

Improve the UX of credential generator validation logic.

Passphrase:

• Validated fields that allow freehand editing (length, separator) only trigger generations when they're valid.
• If a freehand field is invalid and loses focus, the field resets to its last-valid value and triggers generation.
• If a checkbox field is adjusted and any field is invalid, the field resets to its last-valid value and triggers validation.
• If a field is invalid and the user clicks the "generate" button, the field resets to its last-valid value and triggers validation.

Note: At present, this is only implemented for passphrase options. If the revised behavior is suitable, then it'll be ported to other credential settings panels.

📸 Screenshots

TBD

🦮 Reviewer guidelines

• 👍 (:+1:) or similar for great changes
• 📝 (:memo:) or ℹ️ (:information_source:) for notes or general info
• ❓ (:question:) for questions
• 🤔 (:thinking:) or 💭 (:thought_balloon:) for more open inquiry that's not quite a confirmed issue and could potentially benefit from discussion
• 🎨 (:art:) for suggestions / improvements
• ❌ (:x:) or ⚠️ (:warning:) for more significant problems or concerns needing attention
• 🌱 (:seedling:) or ♻️ (:recycle:) for future improvements or indications of technical debt
• ⛏ (:pick:) for minor or nitpick changes

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 33.54%. Comparing base (dd6def2) to head (4f76d0f).
Report is 1 commits behind head on main.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
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  Coverage   33.54%   33.54%           
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  Files        2810     2810           
  Lines       87329    87329           
  Branches    16658    16658           
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  Hits        29292    29292           
  Misses      55740    55740           
  Partials     2297     2297           

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[audreyality]

Superceded by #11816.