Add gene-shapes module

src/scripts/component/sequence/gene-shapes.ts

+import { GeneData } from "./gene";
+import { ScaleLinear } from "d3-scale";
+
+export function arrowShape(data: GeneData, xScale: ScaleLinear<number, number>, geneHeight: number) {
+    const geneWidth = xScale(data.length);
+    return "M 0 0 V " + (-geneHeight) + " H " + geneWidth + " V " + geneHeight + " H " + (-geneWidth) + " Z";
+}
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