Additional vtable tests/benchmarks

[avanhatt]

More tests exercising dyn Trait functionality, particularly with:

• Potentially conflicting names.
• Multiple traits and levels of nesting.
• Traits + generics (Only object safe/only static?)
• Traits with where clauses.
• Pulling code with traits from real open source examples.

[avanhatt]

Added 4 new tests for duplicate dyn trait names in ff4b095.

[avanhatt]

New nested trait tests in #176

[avanhatt]

Minimal examples from open source added in #278, #268, #261.