fluent 0.16.2 contains breaking changes

`fluent` 0.16.2 changed its `fluent-bundle` dependency from 0.15.3 to 0.16. `fluent-bundle` 0.16.0 changed its `fluent-syntax` dependency from 0.11.1 to 0.12. `fluent` has types from `fluent-syntax` (at least `ast::Pattern` and `ast::Entry`) in its public API, so that `fluent` 0.16.1 uses types from `fluent-syntax` 0.11 while `fluent` 0.16.2 uses types from `fluent-syntax` 0.12. This is a breaking change as they are technically different types. The issue manifests at least in `i18n-embed` (0.15.4) as it uses `fluent` 0.16 with types from `fluent-syntax` 0.11. This works fine with 0.16.1 (and I suppose 0.16.0), but breaks with 0.16.2 which expects `fluent-syntax` 0.12 types. Reproducer: ```sh cargo init cargo add i18n-embed -F fluent-system cargo build 💥 ```