Merge Passkey and Autofill settings

### Checks

- [x] I have read the Wiki, searched the open issues, and still think this is a new feature.

### Explain the problem clearly and succinctly:

_No response_

### Describe the solution you'd like:

Several settings are equivalent between Passkey and Autofill, so it is best to merge them into the same page.

### Describe alternatives you've considered:

_No response_

### Additional context:

_No response_

Start by locating the Passkey and Autofill settings pages and comparing which settings are equivalent. Determine the intended shared page structure and confirm that the merged page exposes the equivalent settings without duplication.

Written by the indexing model from the issue text.