* Add file context to minifier errors when publishing
* Misc fixes (see issues)
* Allow custom server error template in layouts/server/error.html
To get to this, this commit also cleans up and simplifies the code surrounding errors and files. This also removes the usage of `github.com/pkg/errors`, mostly because of https://github.com/pkg/errors/issues/223 -- but also because most of this is now built-in to Go.
Fixes#9852Fixes#9857Fixes#9863
The old implementation had some issues, mostly related to the context (e.g. name, file paths) passed to the template.
This new implementation is using the exact same code path for evaluating the pages as in a regular build.
This also makes it more robust and easier to reason about in a multilingual setup.
Now, if you are explicit about the target path, Hugo will now always pick the correct mount and language:
```bash
hugo new content/en/posts/my-first-post.md
```
Fixes#9032Fixes#7589Fixes#9043Fixes#9046Fixes#9047
