Fix using static behavior for anonymous enums

[reflectronic]

Do not use the mangled anonymous name in using static directives. Additionally, a using static directive should not be added when members of the enum are already available in context (for example, when inside the method class.)

[tannergooding]

@reflectronic are you interested in taking this forward still?

[reflectronic]

Looks like the tests I added are passing in main as-is, so I'll just update this PR to add these tests (anonymous enums seem to be untested currently).