feat(component): enable custom text rendering in PortableText

[theisel]

Provides users with fine-grained control over text node output via the new text option.

// pages/some-page.astro
---
import { PortableText } from "astro-portabletext";
import TextReplace from '@/components/TextReplace.astro';
---

<PortableText value={/* Portable Text blocks */} components={{text: TextReplace}}/>

// TextReplace.astro
---
import type { TextNode, Props as $ } from "astro-portabletext/types";

export type Props = $<TextNode>;

const { node } = Astro.props;
const replacedText = node.text.replace('panda', '🐼');
---

{replacedText}