Suggestion: Allow configurable set of uri prefixes to be parsed as urls for link tags

TSDoc currently only treats a {@link} tag's destination as a URL if it starts with scheme://. I would suggest widening this via configuration to allow a limited set of prefixes to be treated as URLs. This would allow for the use of {@link} tags that point at documentation IDs in tools like DocFX (including documentation IDs from merged documentation sources that are not in the model):

tsdoc.json

{
  "linkUrlPrefixes": ["xref", "mailto"]
}

foo.d.ts

import { Bar } from "mypackage";

/**
 * Returns a {@link xref:mypackage!Bar:class|Bar}.
 * @remarks
 * If we need to return something else, email {@link mailto:bob@foo.com|Bob}.
 */
export function foo(): Bar;

Begin by tracing how {@link} destinations are recognized and how tsdoc.json configuration is handled. Use the xref and mailto examples in foo.d.ts as behavioral cases; done means configured prefixes are accepted as URL destinations while unconfigured parsing remains unchanged.