Previously, the `NotFound` status code was used to signal many kinds of
recoverable, forwarding errors. This included validation errors, incorrect
Content-Type errors, and more.
This commit modifies the status code used to forward in these instances to more
precisely indicate the forwarding condition. In particular:
* Parameter `FromParam` errors now forward as 422 (`UnprocessableEntity`).
* Query paramater errors now forward as 422 (`UnprocessableEntity`).
* Use of incorrect form content-type forwards as 413 (`UnsupportedMediaType`).
* `WebSocket` guard now forwards as 400 (`BadRequest`).
* `&Host`, `&Accept`, `&ContentType`, `IpAddr`, and `SocketAddr` all forward
with a 500 (`InternalServerError`).
Additionally, the `IntoOutcome` trait was overhauled to support functionality
previously offered by methods on `Outcome`. The `Outcome::forward()` method now
requires a status code to use for the forwarding outcome.
Finally, logging of `Outcome`s now includes the relevant status code.
Resolves#2626.
The primary motivation is to deconflate the leading `F`s in `Failure` and
`Forward`. In particular, when using a generics, we used `F` for forward, which
could easily be confused for `F` for `Failure`. This resolves the conflation.
Previously, `dyn_templates` walked the user-provided `template_dir` path by
constructing a glob pattern prefixed with `template_dir`. If `template_dir`
contained characters recognized by the glob pattern parser, then at best the
pattern failed to parse, and at worst, incorrect directories were searched.
This commit removes the use of `glob` to walk the templates directory and
instead uses `walkdir`, obviating the issues described above.
Fixes#2627.