feat(viewport-options): add interpolate

examples/svelte/src/routes/examples/usesvelteflow/Sidebar.svelte

@@ -31,7 +31,9 @@
 	<button onclick={() => zoomOut({ duration: 1000 })}>zoom out transition</button>
 	<button onclick={() => setZoom(2)}>set zoom</button>
 	<button onclick={() => fitView({ duration: 600 })}>fitView</button>
-	<button onclick={() => fitView({ duration: 600, ease: (t) => +t })}>fitView linear</button>
+	<button onclick={() => fitView({ duration: 600, ease: (t) => +t, interpolate: 'linear' })}
+		>fitView linear</button
+	>
 	<button onclick={() => setCenter(0, 0)}>setCenter 0, 0</button>
 	<button onclick={() => setViewport({ x: 100, y: 100, zoom: 2 })}>setViewport</button>
 	<button onclick={() => console.log(getViewport())}>getViewport</button>