[feat] experimental support for ARROW:extension:point

[igorDykhta]

• adds support for ARROW:extension:name EXTENSION_NAME.POINT position columns in Point, Line, Arc, Text layers.
• can pick geoarrow point column as source for Heatmap layer.
• interleaved xy geoarrow point vector is passed directly as a position data attribute for rendering.
• separate lon / lat columns are converted to geoarrow point vectors (only when source file is an .arrow file).
• this PR doesn't affect existing loading and support of non-geo columns.

Known issues:

• text layer supplied with ARROW:extension:point column can only render string arrow columns (no values offsets).
• figure out how to store an Arrow table in Arrow Data containers, and to update it properly with progressive loading.

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