On macOS, WKWebView applies system auto-capitalization to text inputs, so
typing a lowercase rule payload (e.g. a domain) in the rule editor dialog
turned its first letter into uppercase and required a manual correction.
Apply the same input-hint attributes already used by other text fields in
the app (autoComplete/autoCorrect/autoCapitalize/spellCheck) to the rule
content field.
Fixes#8038
