fix(parse5-utils): add support for templates

[WillsonSmith]

Proposed fix for #2397

parse5-utils does not currently handle tags within a <template> tag, this prevents rollup-plugin-html from extracting assets that are within a template.

What I did

1. Add a condition to findNodes that will get child nodes of a <template> tag
2. Add a test to ensure the change functions as expected

🤔 I suppose this might be a major version bump.

[changeset-bot]

🦋 Changeset detected

Latest commit: d5da0e4

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

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Name	Type
@web/parse5-utils	Patch

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[koddsson]

@43081j; You've been doing parse5 stuff lately? What do you think?

[43081j]

Makes sense to me!

I've been building an official parse5 tools package but we can't move mw over yet since it doesn't build esm.

Once we can use that, you would still do this same code though. But there's a type guard to check if a node is a template