Feature: add support for shiki defaultColors option

[madcampos]

Changes

This add support for for the defaultColor option from shiki. It exposes the option both to the internal highlighter and to astro's config.

Resolves: #11238

Testing

Two unit tests were added to ensure the setting is respected.

Docs

I think a reference to shiki's docs will help. Will create a PR to add the doc reference soon.

/cc @withastro/maintainers-docs for feedback!

PS: Thanks to @0916dhkim and @ettavolt for the help with the code

[changeset-bot]

🦋 Changeset detected

Latest commit: 29f056e

The changes in this PR will be included in the next version bump.

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[github-actions]

This PR is blocked because it contains a minor changeset. A reviewer will merge this at the next release if approved.

[bluwy]

Looks great. Awesome work!

[sarah11918]

Just placeholding for docs here!

[matthewp]

Thanks @madcampos, we will need docs in order to get this into 4.12. Thanks!

[madcampos]

Sorry for the delay folks, here is the docs PR: withastro/docs#8722

[sarah11918]

Thank you for providing the docs PR, @madcampos ! Based on that, here's an idea for the changeset message. For minor releases, we don't mind if they are a little longer since people will often (excitedly!) read them to learn about what's new. Let's take the opportunity to sell this a little bit, eh!

[sarah11918]

Suggested change

	Enable the "defaultColor" option from shiki
	Adds support for [Shiki's "defaultColor" option](https://shiki.style/guide/dual-themes#without-default-color).
	This option allows you to override the values of a theme's CSS variables and use your own colors.
	Configure `defaultColor: false` in your Shiki config to apply throughout your site, or pass to Astro's built-in `<Code>` component to style an individual code block.
	```js title="astro.config.mjs"
	import { defineConfig } from 'astro/config';
	export default defineConfig({
	markdown: {
	shikiConfig: {
	themes: {
	light: 'github-light',
	dark: 'github-dark',
	},
	defaultColor: false,
	},
	},
	});
	```
	```js
	---
	import { Code } from 'astro:components';
	---
	<Code code={`const useMyColors = true`} lang="js" defaultColor=false />

OK, thanks for waiting! I'm not sure whether all of this is entirely accurate, but this is the general style of message I'm thinking of here. So, using this as a model, can you make this accurate/appropriate? I think this would be a helpful way to introduce this new option!

[madcampos]

Thank you for the suggestion! I've added a couple small changes. I hope that is okay

[sarah11918]

Yup, and I just updated some grammar and it's great, thank you!

[sarah11918]

Approving for docs!