Re-explore scoped variants

[paarthenon]

Scoped variants, while functional, were created before TS had template literal types. Now that we live in that world, there are most likely better ways to implement scoped variants and more powerful functionality we can include. Perhaps better support for arbitrary separators.

There's also a conversation to be had on what would make the best separators. Some candidates would be

• ., probably my current favorite. It's clear and concise, but because it's so commonly used to scope things people may already be in the habit of using foo.bar.baz as a key. That would break the functionality intended to separate variant scopes, so another separator might be preferred.
• ::, classic from C++ and more.
• | I personally enjoy the aesthetic but more commonly used to pipeline.
• -
• /

[paarthenon]

As I revisit this I feel that it is worthwhile but should not prevent the release of 3.0. Please feel free to provide feedback if this is more urgent than I expect or if you would like to contribute. Until then I feel this can be introduced in future 3.X releases.