php-language-features: Add html indent rule

[Abdillah]

This PR fixes #62077.

Testing the change

1. Create new file.
2. Change file type to PHP.
3. Type in some nested matching html tags without manually indenting the line:

a. Without the change.

<div>
<div>
</div>
</div>

b. With the change.

<div>
    <div>
    </div>
</div>

[msftclas]

All CLA requirements met.

[roblourens]

I think this issue is different than I thought it was, since it starts working as soon as the html extension is activated. @aeschli so the onLanguage:html activationEvent is only triggered when a .html file is opened, even though the html language configuration applies to parts of a php file? Do you think we should add onLanguage:php to the html extension?

[Abdillah]

Do two extensions allowed to share each other code (like sharing one server)? If we can make sure both HTML and PHP extension server recognize embedded PHP, Javascript, and CSS, that would be ideal IMO. Before that implementation, I think it's a lossless trade to solve smaller issue first.

But I don't think that HTML extension parse PHP language. It should switch to PHP when recognize the syntax, or just give warning.

_{I am new here might not get the context right}

[Abdillah]

Turns out the PHP already support Javascript and CSS. I am not aware of this just by looking at the code. Is there any HTML ext. activation in PHP language mode somewhere? I understand now, it is in the basic plugin and how everything put together.

I've also tested the onLanguage:php solution too and it works well. Moreover, we can easily provide auto-closing completion (#76800) as well.

[aeschli]

PHP defines HTML as an embedded language here: https://github.com/microsoft/vscode/blob/master/extensions/php/package.json#L44. The bug is that VSCode doesn't activate 'html' when it needs it's indent rules. As HTML defines the indent rules in code, activation is necessary.

It's a VSCode issue. I suggest to create a new issue and assign it to @alexdima.

The PR is not good, PHP must not define any html settings, it will cause conflicts. PHP could define a new language php-html, use that for embedding and define rules for that. But I wouldn't do that as it leads to duplication.

[roblourens]

Oh, I get it. Thanks @aeschli. Filed #98621