Provide HTML support for Qute HTML templates

[fbricon]

Currently, Qute html templates only get Qute support. HTML validation and completion are missing. Would be nice if we could hook up the HTML LS to qute-html templates.

[angelozerr]

I have created the issue microsoft/vscode#131531

But it will be not perfect because we will have html completion in qute expression.

Is it really annoying?

An another solution is to create a custom langage server which managés html by using vscode html kanguage service. I fera that it us à big work.

If the first solution can be acceptable I will try to create a pr in vscode

[angelozerr]

I created a PR in vscode microsoft/vscode#146731

Let's wait feedback.

[angelozerr]

My PR from vscode microsoft/vscode#146731 has been merged!

For the moment VSCode Insiders doesn't contains this feature. I'm wiating for that to test my draft PR #527