Add support for shiny express apps #1539

Job	Run time
test-jupyter	6m 4s
test (py3.7 ubuntu-latest)	1m 7s
prerelease-test	1m 8s
Integration tests against latest Connect	3m 9s
test (py3.8 ubuntu-latest)	1m 5s
test (py3.9 ubuntu-latest)	1m 5s
test (py3.10 ubuntu-latest)	1m 3s
test (py3.11 ubuntu-latest)	1m 7s
test (py3.12 ubuntu-latest)	2m 40s
test (py3.9 macos-latest)	4m 12s
test (py3.9 windows-latest)	2m 47s
docs	34s
distributions	50s
dispatch	0s
	26m 51s

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