docs(errorDisplay): encode `<` and `>` in error messages

When an error message contains an HTML string (e.g. `$location:nobase` containing `<base>`), it was
interpreted as a literal HTML element, instead of text. Error messages are not expected to render
as HTML, but we still need to use `.html()` in `errorDisplay`, so that the links created by
`errorLinkFilter` are properly displayed.
This commit solves this issue by replacing `<`/`>` with `&lt;`/`&gt;`.

Related to #14016.