Tie use of feature to the current edition

[nikomatsakis]

Today we use the #![feature] to decide whether to use new-style capture, but we should also consider the 2021 edition.

[arora-aman]

• We'd probably want to look into tying the lint to edition as well

[m-ou-se]

Is there anything blocking this?

[nikomatsakis]

I'm going to assign this to @arora-aman -- feel free to reassign.

[arora-aman]

• Feature enabled by default on edition 2021
• Set future incompabile in lint metadata to edition 2021

[m-ou-se]

For the lint:

• Change the lint name to something that reads well in allow() and deny(). (What exactly does it allow or deny?)
  • Happening in Rename some Rust 2021 lints to better names  rust#86717
• Mark it as future_incompatible: Make disjoint_capture_migration an edition lint. rust#86673
• Refer to Rust 2021 instead of the unstable feature name: Make disjoint_capture_migration an edition lint. rust#86673
  • in the lint messages: Make disjoint_capture_migration an edition lint. rust#86673
  • in the lint documentation: Make disjoint_capture_migration an edition lint. rust#86673
• Add a link to the edition guide: Make disjoint_capture_migration an edition lint. rust#86673

[nikomatsakis]

This is now done.