[FEATURE] Touch measurements

[xeolabs]

This PR adds touch support for creating distance and angle measurements, with optional snapping to the nearest vertex or edge.

Creating DistanceMeasurements with Touch Input

In the following example, we'll create distance measurements with touch input, with snapping
to the nearest vertex or edge. While creating the measurements, a long-touch when setting the
start or end point will cause the point to snap to the nearest vertex or edge. A quick
touch-release will immediately set the point at the tapped position on the object surface.

[Run example]

import {Viewer, XKTLoaderPlugin, DistanceMeasurementsPlugin, DistanceMeasurementsTouchControl} from "xeokit-sdk.es.js";

const viewer = new Viewer({
    canvasId: "myCanvas",
    transparent: true
});

viewer.scene.camera.eye = [-2.37, 18.97, -26.12];
viewer.scene.camera.look = [10.97, 5.82, -11.22];
viewer.scene.camera.up = [0.36, 0.83, 0.40];

const xktLoader = new XKTLoaderPlugin(viewer);

const distanceMeasurements = new DistanceMeasurementsPlugin(viewer);

const model = xktLoader.load({
     src: "./models/xkt/duplex/duplex.xkt"
});

const distanceMeasurements = new DistanceMeasurementsPlugin(viewer);

const distanceMeasurementsTouchControl  = new DistanceMeasurementsTouchControl(distanceMeasurements, {
    pointerLens : new PointerLens(viewer),
    snapToVertex: true,
    snapToEdge: true
})

distanceMeasurementsTouchControl.activate();

Creating AngleMeasurements with Touch Input

In the following example, we'll create angle measurements with touch input, with snapping
to the nearest vertex or edge. While creating the measurements, a long-touch when setting the
start, corner or end point will cause the point to snap to the nearest vertex or edge. A quick
touch-release will immediately set the point at the tapped position on the object surface.

[Run example]

import {Viewer, XKTLoaderPlugin, AngleMeasurementsPlugin, AngleMeasurementsTouchControl} from "xeokit-sdk.es.js";

const viewer = new Viewer({
    canvasId: "myCanvas",
    transparent: true
});

viewer.scene.camera.eye = [-2.37, 18.97, -26.12];
viewer.scene.camera.look = [10.97, 5.82, -11.22];
viewer.scene.camera.up = [0.36, 0.83, 0.40];

const xktLoader = new XKTLoaderPlugin(viewer);

const angleMeasurements = new AngleMeasurementsPlugin(viewer);

const model = xktLoader.load({
     src: "./models/xkt/duplex/duplex.xkt"
});

const angleMeasurements = new AngleMeasurementsPlugin(viewer);

const angleMeasurementsTouchControl  = new AngleMeasurementsTouchControl(angleMeasurements, {
    pointerLens : new PointerLens(viewer),
    snapToVertex: true,
    snapToEdge: true
})

angleMeasurementsTouchControl.activate();