Add volar-service-yaml

[remcohaszing]

This provides all features from the YAML language service through Volar.

It could be interesting to add support for the JSON schemastore later. I omitted this for now, as that’s part of the language server, not the language service.

[johnsoncodehk]

We don't need to handle http requests in the service because it is already handled in language server: https://github.com/volarjs/volar.js/blob/fc0bc2c262e693b6d41e87bff758ac1eb6eeb8c9/packages/language-server/src/node/index.ts#L54

[johnsoncodehk]

I found this is simpler than json service. The following code of json service is modified from vscode implementation. But I think your implementation also works, let's keep it.

services/packages/json/src/index.ts

Lines 21 to 32 in a2eee58

	resolveRelativePath: (ref: string, base: string) => {
	if (ref.match(/^\w[\w\d+.-]*:/)) {
	// starts with a schema
	return ref;
	}
	if (ref[0] === '/') { // resolve absolute path against the current workspace folder
	return base + ref;
	}
	const baseUri = URI.parse(base);
	const baseUriDir = baseUri.path.endsWith('/') ? baseUri : Utils.dirname(baseUri);
	return Utils.resolvePath(baseUriDir, ref).toString(true);
	},

[johnsoncodehk]

This is a good way to avoid downstream bundling hack! But since this is inconsistent with other services, I will temporarily change it to import from 'yaml-language-server' and change to import from umd path for all services in a separate PR, so we can retrace the reason.

[johnsoncodehk]

Sorry for the long delay, thanks a lot for the work!