[Rust] Fix enum variant name generation

[whirm]

Found out that oneOf's enum variant names were not correctly generated and datatypes like Vec<foo::bar::Baz> would end up as Baz instead of VecOfBaz generating duplicates in cases like the test included.

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[whirm]

I found this case where an enum with identically named variants ends up being generated.

Edit: Working on a fix

[whirm]

@frol, @farcaller, @richardwhiuk, @paladinzh, @jacob-pro Ready to review!

[wing328]

thanks for the PR

cc @linxGnu

[linxGnu]

LGTM