Zoom handler event affects animations

[btzr-io]

Describe the bug
The zoom handler function makes the zoom animations choppy and slow.
I suspect is caused by the new implentation on the getTargetZoom function.

To Reproduce
Steps to reproduce the behavior:

1. Use the wheel mouse button to zoom in / out.
2. See animations.

Expected behavior
Smooth zoom animations

Villain/src/components/render.js

Lines 165 to 174 in 448b559

	this.viewer.addHandler('zoom', ({ zoom }) => {
	const { viewport } = this.viewer
	const max = viewport.getMaxZoom()
	const min = viewport.getMinZoom()
	const currentZoom = parseInt((zoom / this.getTargetZoom()) * 100)
	const canZoomIn = zoom < max && currentZoom < 100
	const canZoomOut = zoom > min
	this.context.updateState({ currentZoom, canZoomIn, canZoomOut })
	})

See: Optimize getTargetZoom function #67

[Brostafa]

@btzr-io #73

[btzr-io]

Update

The issue appears to be more noticeable on firefox I tested on chrome, brave and electron and its working really smooth.

[btzr-io]

Not sure if this is related: openseadragon/openseadragon#1078

[btzr-io]

This require more work and testing.