Use the new PageStyle datatype instead of page style string literals

[rvanbekkum]

If runtime 14.0 or newer is used (BC25.0 or newer), then check for any occurences of string literals 'Unfavorable', 'Favorable', ... (and all other supported page styles).
Raise a diagnostic on the string literal and suggest to use the new PageStyle datatype instead (e.g., PageStyle::Unfavorable).
Also raise the diagnostic for Label variables like Label 'Unfavorable', Locked = true

Adopting the use of the new PageStyle datatype allows to more easily get the supported pagestyles via IntelliSense and avoids incorrect behaviour when a typo is made in hardcoded strings or label variables.
Unfortunately the StyleExpr property on page controls still only accepts strings (or booleans), so a conversion to a string will still be needed, e.g., Format(MyPageStyleVariable)

Content of this idea might also be good for alguidelines.dev