[clang][cli] Let denormalizer decide how to render the option based on the option class

Before this patch, you needed to use `AutoNormalizeEnumJoined` whenever you wanted to **de**normalize joined enum.
Besides the naming confusion, this means the fact the option is joined is specified in two places: in the normalization multiclass and in the `Joined<["-"], ...>` multiclass.
This patch makes this work automatically, taking into account the `OptionClass` of options.

Also, the enum denormalizer now just looks up the spelling of the present enum case in a table and forwards it to the string denormalizer.

I also added more tests that exercise this.

Reviewed By: dexonsmith

Original patch by Daniel Grumberg.

Differential Revision: https://reviews.llvm.org/D84189