Update vega to 5.27.0 and vega-themes to 2.14.0 #442

Job	Run time
rust-fmt-clippy	5m 21s
cargo-bundle-license	1m 5s
codegen-clean	55s
black-lint	12s
vl-convert-python-tests (ubuntu-latest, 3.10, bash -l {0})	10m 57s
vl-convert-rs-tests (ubuntu-latest)	14m 28s
vl-convert-rs-tests (windows-2022)	15m 26s
vl-convert-python-tests (windows-2022, 3.10, pwsh)	17m 21s
vl-convert-rs-tests (macos-11)	15m 46s
vl-convert-python-tests (macos-11, 3.10, bash -l {0})	18m 35s
	1h 40m 6s

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