v2: Add VegaFusionWidget based on AnyWidget #971

Job	Run time
build-vegafusion-python-linux-64	14m 54s
build-vegafusion-python-osx-64	21m 41s
build-vegafusion-python-osx-arm64	14m 14s
build-vegafusion-python-linux-arm64	15m 54s
build-vegafusion-python-win-64	30m 33s
build-vegafusion-server-linux-64	13m 32s
build-vegafusion-server-linux-arm64	14m 47s
build-vegafusion-server-osx-64	2h 27m 29s
build-vegafusion-server-win-64	30m 25s
build-vegafusion-wasm	10m 50s
check-rust	7m 45s
build-vegafusion-server-osx-arm64	12m 50s
test-rust (ubuntu-20.04)	25m 53s
test-rust (windows-2022)	48m 19s
test-rust (macos-14)	27m 48s
test-vegafusion-python-osx-arm64	34s
test-vegafusion-python-linux-64	31m 24s
test-vegafusion-python-win-64	1m 58s
	7h 50m 50s

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