deprecate use-foo style feature flags in favor of just foo

[michaelkirk]

Rust 1.60 introduced the dep:foo syntax, which removed the ambiguity between a feature name and an optional crate name, so we no longer need the use- prefix.

Let's change it and deprecate the old ones.

[michaelkirk]

I don't know that there's actually any good way of showing a deprecation warning when building with a deprecated feature flag. Anyone know any tricks?

rust-lang/cargo#7130
rust-lang/rfcs#3486

[lnicola]

Mark Geometry and friends as deprecated when the feature flags are set 😅.

[michaelkirk]

You brute! But that might work... 😄

[urschrei]

That's incredibly horrible and I love it.