feat(vim): Add test case to sanity-test all Vim settings

[bryphe]

Part of the VimL compatibility work - validate that we can read & set all the Vim settings that are available in libvim.

There is still work to hook these up to be functional, but ensuring that they can be read/set is an important first step.

Will also need similar tests to validate Ex commands and VimL function calls.

TODO:

• Add remaining configuration
• Remove some unnecessary settings (ie, ballooneval) from libvim
• Add set-value tests