Ensures key is properly propagated to importedElements

[shawncrawley]

Fixes #1270. The "key" prop was being lost in the trickle-down of importedElements.

Description

I just added a block of code to the createAttributes function to check if the "key" is part of the vdom model and if so, to add it to the attributes. There may be a better and more thorough way to do this higher up the call chain, but this fixed the issue for me in my use case (see #1270).

Checklist

Please update this checklist as you complete each item:

• Tests have been developed for bug fixes or new functionality.
• The changelog has been updated, if necessary.
• Documentation has been updated, if necessary.
• GitHub Issues closed by this PR have been linked.

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[Archmonger]

Can you add a test for this within src/reactpy/tests/test_web/test_module.py?

You can directly use the GridLayout component if you'd like.