feat: add DensityMap trace for the MapLibre map subplot #232

Job	Run time
semver	49s
Build Wasm Examples (callback-example)	1m 5s
Tests (windows-latest, chrome, plotly_ndarray,plotly_image,static_export_chromedriver,debug)	8m 19s
Rustfmt	18s
Tests (macos-latest, chrome, plotly_ndarray,plotly_image,static_export_default,debug)	5m 22s
Clippy	5m 30s
Build Wasm Examples (basic)	1m 1s
Build Examples (customization/density_mapbox_example)	33s
Tests (ubuntu-latest, firefox, plotly_ndarray,plotly_image,static_export_geckodriver,static_expor...	3m 22s
Code Coverage	11s
Build Examples (images)	52s
Build Examples (basic_charts)	37s
Tests (ubuntu-latest, chrome, plotly_ndarray,plotly_image,static_export_default,debug)	3m 17s
Build Examples (scientific_charts)	33s
Build Book	4m 28s
Build Examples (customization/multiple_plots_example)	36s
Build Examples (kaleido)	1m 14s
Build Examples (financial_charts)	38s
Build Examples (maps)	59s
Build Examples (ndarray)	36s
Build Examples (themes)	35s
Build Examples (customization/consistent_static_format_export)	2m 2s
Build Examples (custom_controls)	35s
Build Examples (subplots)	35s
Build Examples (shapes)	34s
Build Examples (statistical_charts)	38s
Build Examples (3d_charts)	33s
	45m 52s

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