Use deno_core::JSError in deno

[ry]

src/js_errors.rs takes care of source maps and color while
core/js_errors.rs is just the basic struct.

[piscisaureus]

Un-enthousiastic LGTM.
struct JSErrorColor seems fishy to me and duplicates code between core and that root crate. I think this should be done by adding a different trait but I'm unsure how.

[ry]

I also am not super happy with it, but wrapping was the suggested (actually only) way of modifying a Display on a struct.
See https://users.rust-lang.org/t/reusing-an-fmt-formatter/8531/4

I could of course shadow the original name in src/ instead of calling it JSErrorColor, but I think this is less explicit and confusing. Also users won't be able to access member information.