add missing re-exports for layout types #566

Job	Run time
Clippy	3m 2s
Rustfmt	13s
Build Book	1m 34s
Build Wasm Examples (basic)	49s
Tests (windows-latest)	3m 57s
Build Wasm Examples (callback-example)	48s
Tests (macos-latest)	2m 33s
semver	43s
Tests (ubuntu-latest)	2m 21s
Code Coverage	13s
Build Examples (customization)	25s
Build Examples (custom_controls)	23s
Build Examples (basic_charts)	33s
Build Examples (3d_charts)	25s
Build Examples (scientific_charts)	23s
Build Examples (ndarray)	31s
Build Examples (financial_charts)	24s
Build Examples (kaleido)	1m 9s
Build Examples (subplots)	22s
Build Examples (images)	39s
Build Examples (themes)	26s
Build Examples (shapes)	25s
Build Examples (maps)	37s
	22m 55s

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