Add support for using .htm instead of .html files

[marvinhagemeister]

Thanks to @danielweck who found all the places we need to update to support this 👍

Fixes #471

[changeset-bot]

🦋 Changeset detected

Latest commit: 4b35b8f

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

This PR includes changesets to release 2 packages

Name	Type
@wmr-plugins/nomodule	Minor
wmr	Minor

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[github-actions]

Size Change: +2 B (0%)

Total Size: 694 kB

Filename	Size	Change
packages/wmr/wmr.cjs	661 kB	+2 B (0%)

ℹ️ View Unchanged

Filename	Size	Change
examples/demo/dist/about/index.html	668 B	0 B
examples/demo/dist/assets/Calendar.********.css	702 B	0 B
examples/demo/dist/assets/style.********.css	386 B	0 B
examples/demo/dist/chunks/class-fields.********.js	201 B	0 B
examples/demo/dist/chunks/compat.********.js	15.3 kB	0 B
examples/demo/dist/chunks/index.********.js	303 B	0 B
examples/demo/dist/chunks/json.********.js	237 B	0 B
examples/demo/dist/chunks/prerender.********.js	2.41 kB	0 B
examples/demo/dist/class-fields/index.html	647 B	0 B
examples/demo/dist/compat/index.html	1.5 kB	0 B
examples/demo/dist/env/index.html	724 B	0 B
examples/demo/dist/error/index.html	657 B	0 B
examples/demo/dist/files/index.html	688 B	0 B
examples/demo/dist/index.********.js	7.23 kB	0 B
examples/demo/dist/index.html	715 B	0 B
examples/demo/dist/json/index.html	667 B	0 B
examples/demo/dist/lazy-and-late/index.html	669 B	0 B

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