fix(ssr): add comments to the output of lwc:if blocks @W-16946260

[wjhsf]

Details

When you use lwc:if, the rendered output contains empty HTML comments. For example,

<template lwc:if={isTrue}>
The rain in Spain falls mainly in the plain.
</template>

becomes

<!---->
The rain in Spain falls mainly in the plain.
<!---->

This PR adds that functionality to the SSR compiler.

Note: This PR is a continuation of the work to add missing directives, so it is built on #4615. Also, it turns out that we don't need to implement ElseifBlock or ElseBlock because they seem to be handled by IfBlock.

Does this pull request introduce a breaking change?

• 😮‍💨 No, it does not introduce a breaking change.
• 💔 Yes, it does introduce a breaking change.

Does this pull request introduce an observable change?

• 🤞 No, it does not introduce an observable change.
• 🔬 Yes, it does include an observable change.

GUS work item

W-16946260