Fix wheel build

[randombenj]

This PR should fix the wheel build.

$ python -m build
...
error: can't copy 'captum/insights/attr_vis/widget/static/extension.js': doesn't exist or not a regular file

ERROR Backend subproccess exited when trying to invoke build_wheel

This was also an issue in the past (https://github.com/pytorch/captum/issues/284), so I added a ci step to test the wheel build.

[randombenj]

Failing tests after rebase seem unrelated to the changes on this PR ...

edit: not failing after second rebase :)

[facebook-github-bot]

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