[cpp-rest-sdk] fix enum values being used instead of names

[aminya]

This fixes the issue with enum values being used instead of enum names. This is problematic when the values contain symbols that can't be a C++ variable.

It also simplifies the enum variables by removing the unnecessary prefix for scoped enum classes.

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[wing328]

can you please resolve the merge conflicts when you've time?

also looks like this is a breaking change

i remember someone added the classname prefix with a reason. need to find out more before we can merge this PR.

update: the change was made a while ago. what about adding an option for fallback?

[aminya]

@wing328 It's a breaking change cause it fixes the issue of using values instead of names. This will not work for any strings that are not symbols, such as numbers or names with dashes or dots.

I don't think we should keep this compatible, as it was broken, and only worked because the tests assumed symbol-like string options. The prefix is unnecessary because in C++, the enum classes are scoped.