If user code has a type alias (or custom type) called `Result` or
`Option` etc, this would be used instead of the intended standard
library types causing surprising compile errors from generated code.
Using the fully qualified path allows the generated code to be isolated
from user types.
Includes two basic regression tests covering `Result` and `Send`.
Fixes#1194
- set 1.62 Rust as MSRV
- use new fmt syntax where possible
- refactor `.to_owned()`, `.to_string()` and `.into()` usage
- rename `IntoResolvable::into()` as `IntoResolvable::into_resolvable()` to disambiguate with `Into::into()`
- use `#[derive(Default)]` for enums where possible
- use `bool::then_some()` where possible
