Implements a `bootWordPress()` function aiming to provide a reliable and
consistent boot pipeline for every Playground-based app, whether it's a
browser app, server app, a VS Code extension, or anything else.

As a nice side-effect, Playground can now boot not just from the custom
minified WordPress builds, but also from the official WordPress
releases!

Related issue:
#1398

## How does it work?

`bootWordPress()` ties together all the pieces from different
Playground-based apps. [Boot flow
diagram](#1379 (comment))
demonstrates the idea. A tl;dr pipeline is:

* Mount resources (stage=before WordPress files)
* Unzip WordPress, if that's requested
* Mount resources (stage=before database setup)
* Setup SQLite, MySQL (TODO), or rely on a mounted database
* Run WordPress installer, if the site isn't installed yet

Here's a usage example in a Node.js app:

```ts
const requestHandler = await bootWordPress({
	siteUrl: absoluteUrl,
	createPhpInstance() {
		return new NodePHP();
	},
	createPhpRuntime: async () =>
		await NodePHP.loadRuntime(compiledBlueprint.versions.php),
	wordPressZip,
	sqliteIntegrationPluginZip: fetchSqliteIntegration(monitor),
	sapiName: 'cli',
	createFiles: {
		'/internal/shared/ca-bundle.crt':
			rootCertificates.join('\n'),
	},
	phpIniEntries: {
		'openssl.cafile': '/internal/shared/ca-bundle.crt',
		allow_url_fopen: '1',
		disable_functions: '',
	},
	hooks: {
		async beforeWordPressFiles(php) {
			if (args.mountBeforeInstall) {
				mountResources(php, args.mountBeforeInstall);
			}
		},
	},
});
```

## Testing instructions

* Confirm all the CI checks work
* Load the latest nightly **official WordPress build** into Playground:

http://localhost:5400/website-server/?php=8.0&wp=http://localhost:5400/plugin-proxy.php?url=https://wordpress.org/nightly-builds/wordpress-latest.zip
* Load the official WordPress 6.5 release into Playground:
http://localhost:5400/website-server/?php=8.0&wp=http://localhost:5400/plugin-proxy.php?url=https://wordpress.org/latest.zip
* Confirm Playground CLI still works: Run bun
packages/playground/cli/src/cli.ts server --login and confirm it loads
an installed WordPress.

## Follow-up work

* Replace manual calls to `setupPlatformLevelMuPlugins()` in unit tests
with `bootWordPress()`
* Add unit tests to confirm boot works with minified WordPress build,
official WordPress release, SQLite, MySQL. Test all the `BootOptions`
and confirm PHP.ini directives are used, constants are created etc.
* Remove the `createPhpInstance()` argument in favor of using just the
`PHP` class – once
#1457 merges
* Figure out storing `debug.log` in the `configureErrorLogging`
mu-plugin – right now it's stored in `/wordpress/wp-content`
* Support more database modes: MySQL and `custom` where Playground
relies on `db.php` brought in from
* Replace hooks with a Mount data type that would have different
implementations, like OPFS, Native FS, and Node FS – explorations
started in #1457
* Once the API settles, document the usage for developers

cc @brandonpayton @bgrgicak