Fix "Color by CDS" for BED12 features

[cmdcolin]

Fixes #4772

This adds a phase field to features generated in BED12

The SVG Box renderer uses the existence of the "phase" field to determine whether to color by CDS

Specifically this check

jbrowse-components/plugins/svg/src/SvgFeatureRenderer/components/Box.tsx

Lines 62 to 67 in ce9fb70

	colorByCDS &&
	featureType === 'CDS' &&
	featureStrand !== undefined &&
	featurePhase !== undefined
	) {
	const frame = getFrame(

[cmdcolin]

potentially could remove the check for phase!==undefined as an alternative to this but might just keep for now