feat: allow fallback to defaultRender in render method

[tafelnl]

We can supply linkifyStr with a custom render. Which is quite nice. But if we want to fallback to the default for some reason, that currently requires to copy-paste part of the source code.

For example:

import type { IntermediateRepresentation } from 'linkifyjs';
import linkifyStr from 'linkify-string';

/**
 * The functions `escapeText`, `escapeAttr`, `attributesToString`
 * and `defaultRender` are copied from the source code of linkifyjs.
 */

function escapeText(text: string) {
  return text
    .replace(/&/g, '&')
    .replace(/</g, '&lt;')
    .replace(/>/g, '&gt;');
}

function escapeAttr(href: string) {
  return href.replace(/"/g, '&quot;');
}

function attributesToString(
  attributes: IntermediateRepresentation['attributes']
) {
  const result = [];
  for (const attr in attributes) {
    const val = attributes[attr] + '';
    result.push(`${attr}="${escapeAttr(val)}"`);
  }
  return result.join(' ');
}

function defaultRender({
  tagName,
  attributes,
  content,
}: IntermediateRepresentation) {
  return `<${tagName} ${attributesToString(attributes)}>${escapeText(content)}</${tagName}>`;
}

export function example(value: string, className: string) {
  return linkifyStr(value, {
    className,
    render: {
      url: (options: IntermediateRepresentation) => {
        // some custom logic goes here
        // ...

        if (1 === 1) {
          // some more custom logic
          return '<i>Hello</i>';
        }

        return defaultRender(options);
      },
    },
  });
}

It would be nice to do something like this instead:

import { type IntermediateRepresentation, defaultRender } from 'linkifyjs';
import linkifyStr from 'linkify-string';

export function example(value: string, className: string) {
  return linkifyStr(value, {
    className,
    render: {
      url: (options: IntermediateRepresentation) => {
        // some custom logic goes here
        // ...

        if (1 === 1) {
          // some more custom logic
          return '<i>Hello</i>';
        }

        return defaultRender(options);
      },
    },
  });
}

Or maybe even:

import { type IntermediateRepresentation } from 'linkifyjs';
import linkifyStr from 'linkify-string';

export function example(value: string, className: string) {
  return linkifyStr(value, {
    className,
    render: {
      url: (options: IntermediateRepresentation) => {
        // some custom logic goes here
        // ...

        if (1 === 1) {
          // some more custom logic
          return '<i>Hello</i>';
        }

        return null;
      },
    },
  });
}