get() with index should allow indexes with multiple fields

[xixixao]

It should be possible to use a compound index to query unique ents:

ctx.table("users").get("firstNameLastName", firstName, lastName)

I had trouble getting the types to oblige when I was implementing get() with indexes.

[xixixao]

This is blocked by microsoft/TypeScript#29919 (which should be fixed soon)

[xixixao]

This is fixed on https://github.com/xixixao/convex-ents/tree/variadic-get, will wait for VS Code release with TS 5.4