refactor(core): Homogenize all providers as static

There is no reason to keep an instance of each provider, and moving them
to static like some other one (PointCloudProvider for example) do no
harm, but homogenize all providers to one structure.

Also note that there are two required functions in a provider:
preprocessDataLayer and executeCommand, that are verified when adding a
provider, in the scheduler.

BREAKING CHANGE: KML_Provider and BuildingBox_Provider have been
removed, as well as getPointOrder from WFS_Provider.

src/Core/Scheduler/Providers/3dTiles_Provider.js

@@ -1,5 +1,4 @@
 import * as THREE from 'three';
-import Provider from './Provider';
 import B3dmLoader from '../../../Renderer/ThreeExtended/B3dmLoader';
 import PntsLoader from '../../../Renderer/ThreeExtended/PntsLoader';
 import Fetcher from './Fetcher';
@@ -10,7 +9,6 @@ import Capabilities from '../../System/Capabilities';
 import PrecisionQualifier from '../../../Renderer/Shader/Chunk/PrecisionQualifier.glsl';
 import { init3dTilesLayer } from '../../../Process/3dTilesProcessing';
 
-
 function $3dTilesIndex(tileset, baseURL) {
     let counter = 0;
     this.index = {};
@@ -63,19 +61,7 @@ function $3dTilesIndex(tileset, baseURL) {
     };
 }
 
-function $3dTiles_Provider() {
-    Provider.call(this);
-}
-
-$3dTiles_Provider.prototype = Object.create(Provider.prototype);
-
-$3dTiles_Provider.prototype.constructor = $3dTiles_Provider;
-
-$3dTiles_Provider.prototype.removeLayer = function removeLayer() {
-
-};
-
-$3dTiles_Provider.prototype.preprocessDataLayer = function preprocessDataLayer(layer, view, scheduler) {
+function preprocessDataLayer(layer, view, scheduler) {
     layer.sseThreshold = layer.sseThreshold || 16;
     layer.cleanupDelay = layer.cleanupDelay || 1000;
 
@@ -87,7 +73,7 @@ $3dTiles_Provider.prototype.preprocessDataLayer = function preprocessDataLayer(l
         layer.asset = tileset.asset;
         return init3dTilesLayer(view, scheduler, layer, tileset.root);
     });
-};
+}
 
 function getBox(volume, inverseTileTransform) {
     if (volume.region) {
@@ -159,9 +145,11 @@ export function patchMaterialForLogDepthSupport(material) {
     };
 }
 
-$3dTiles_Provider.prototype.b3dmToMesh = function b3dmToMesh(data, layer, url) {
-    this._b3dmLoader = this._b3dmLoader || new B3dmLoader();
-    return this._b3dmLoader.parse(data, layer.asset.gltfUpAxis, url, this._textDecoder).then((result) => {
+let b3dmLoader;
+let textDecoder;
+function b3dmToMesh(data, layer, url) {
+    b3dmLoader = b3dmLoader || new B3dmLoader();
+    return b3dmLoader.parse(data, layer.asset.gltfUpAxis, url, textDecoder).then((result) => {
         const init = function f_init(mesh) {
             mesh.frustumCulled = false;
             if (mesh.material) {
@@ -189,13 +177,13 @@ $3dTiles_Provider.prototype.b3dmToMesh = function b3dmToMesh(data, layer, url) {
         const object3d = result.gltf.scene;
         return { batchTable, object3d };
     });
-};
+}
 
-$3dTiles_Provider.prototype.pntsParse = function pntsParse(data) {
+function pntsParse(data) {
     return new Promise((resolve) => {
-        resolve({ object3d: PntsLoader.parse(data, this._textDecoder).point });
+        resolve({ object3d: PntsLoader.parse(data, textDecoder).point });
     });
-};
+}
 
 function configureTile(tile, layer, metadata, parent) {
     tile.frustumCulled = false;
@@ -220,14 +208,13 @@ function configureTile(tile, layer, metadata, parent) {
     tile.updateMatrixWorld();
 }
 
-$3dTiles_Provider.prototype.executeCommand = function executeCommand(command) {
+function executeCommand(command) {
     const layer = command.layer;
     const metadata = command.metadata;
     const tile = new THREE.Object3D();
     configureTile(tile, layer, metadata, command.requester);
     const path = metadata.content ? metadata.content.url : undefined;
-    this._textDecoder = this._textDecoder || new TextDecoder('utf-8');
-    const textDecoder = this._textDecoder;
+    textDecoder = textDecoder || new TextDecoder('utf-8');
 
     const setLayer = (obj) => {
         obj.layers.set(layer.threejsLayer);
@@ -236,8 +223,8 @@ $3dTiles_Provider.prototype.executeCommand = function executeCommand(command) {
         // Check if we have relative or absolute url (with tileset's lopocs for example)
         const url = path.startsWith('http') ? path : metadata.baseURL + path;
         const supportedFormats = {
-            b3dm: this.b3dmToMesh.bind(this),
-            pnts: this.pntsParse.bind(this),
+            b3dm: b3dmToMesh,
+            pnts: pntsParse,
         };
         return Fetcher.arrayBuffer(url, layer.networkOptions).then((result) => {
             if (result !== undefined) {
@@ -276,6 +263,9 @@ $3dTiles_Provider.prototype.executeCommand = function executeCommand(command) {
             resolve(tile);
         });
     }
-};
+}
 
-export default $3dTiles_Provider;
+export default {
+    preprocessDataLayer,
+    executeCommand,
+};