compile error (stable): type_alias_impl_trait

[mrghosti3]

This issue is meant for tracking when this feature becomes stable and project could be compiled with stable rust.

Sources:

• https://rust-lang.github.io/impl-trait-initiative/explainer/tait.html
• Tracking issue for RFC 2515, "Permit impl Trait in type aliases" rust-lang/rust#63063

[yshui]

Thank you! Technically we are also using:

• Tracking issue for dyn upcasting coercion rust-lang/rust#65991

But if TAIT got stabilized before trait upcasting, I should be able to get rid of it (we are only upcasting to dyn Any) and enable building with stable rust.