Add HTML comments support

[dirkjonker]

Preact doesn't really support HTML comments, but it is possible to (mis)use it to generate HTML comments anyway, by creating an element with a name that starts with !-- and ends with --, making sure it does not have any attributes. For example, this is being used in Fresh (see denoland/fresh#838) to enable islands. The closing tag of such a "comment" tag however generates invalid HTML, i.e.

h("!--foo--", null, children)

will generate

<!--foo--> ... </!--foo-->

The closing tag: </!-- is invalid HTML and might make it hard for some clients to deal with. Chrome/Firefox have a long track record of magically fixing broken HTML and they turn this into:

<!--!--foo---->

If you plan to programmatically read data from comments (which is a perfectly valid thing to do), you will get some unexpected results as your data will now be prefixed with !-- and suffixed with --.

This change adds "support" for HTML comments by at least not generating invalid HTML.

I'm not 100% sure what kind of change this is, I would think a patch since it's quite the edge case and it fixes rendering invalid HTML in this edge case. But please do correct me if I'm wrong.

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🦋 Changeset detected

Latest commit: dc05abe2722840f5f271063808b6f9dec9af4214

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
preact-render-to-string	Patch

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[dirkjonker]

That makes sense. I'm not using comments myself directly but Fresh uses it as a means to get islands working. Currently that doesn't give any real issues, only the w3 validator gives some warnings about garbage tags.