Makes Enum members implicitly final, refs #5599 (#10852)
refs #5599
This change allows to catch this error by making all Enum members
implicitly Final.
Also modifies Enum plugin, since it was not ready to work
with `Literal[True]` and `Literal[False]`.
Co-authored-by: Shantanu <12621235+hauntsaninja@users.noreply.github.com>
