add missing re-exports for layout types #567

Job	Run time
Rustfmt	14s
Clippy	3m 10s
Tests (windows-latest)	4m 41s
semver	47s
Tests (macos-latest)	3m 7s
Code Coverage	11s
Tests (ubuntu-latest)	2m 18s
Build Book	1m 33s
Build Wasm Examples (callback-example)	59s
Build Wasm Examples (basic)	49s
Build Examples (basic_charts)	27s
Build Examples (customization)	26s
Build Examples (kaleido)	1m 10s
Build Examples (3d_charts)	24s
Build Examples (custom_controls)	24s
Build Examples (scientific_charts)	23s
Build Examples (images)	37s
Build Examples (financial_charts)	27s
Build Examples (themes)	25s
Build Examples (maps)	35s
Build Examples (subplots)	22s
Build Examples (ndarray)	25s
Build Examples (shapes)	25s
	24m 19s

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