Long identifiers will give errors on the format:
```bash
_default/single.html:5:14: executing "main" at <.ThisIsAVeryLongTitl...>: can't evaluate field ThisIsAVeryLongTitle
```
Hugo use this value to match the "base template or not", so we need to strip the "...".
Fixes#5346
`*json.UnmarshalTypeError` and `*json.SyntaxError` has a byte `Offset`, so use that.
This commit also reworks/simplifies the errror line matching logic. This also makes the file reading unbuffered, but that should be fine in this error case.
See #5324
The main item in this commit is showing of errors with a file context when running `hugo server`.
This can be turned off: `hugo server --disableBrowserError` (can also be set in `config.toml`).
But to get there, the error handling in Hugo needed a revision. There are some items left TODO for commits soon to follow, most notable errors in content and config files.
Fixes#5284Fixes#5290
See #5325
See #5324
