Legacy modes should be initiated

[kevinresol]

Because later when used the constructor test is not applied:

nebula.gl/modules/layers/src/layers/editable-geojson-layer.ts

Lines 316 to 318 in 81c8372

	} else if (typeof props.mode === 'string') {
	// Lookup the mode based on its name (for backwards compatibility)
	mode = modeNameMapping[props.mode];

[CLAassistant]

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