Add a new WebGLPointsLayer type using the shader builder utilities

This required adding a `a_index` attribute in the points layer renderer
to be able to make the precomputed shaders to work.

src/ol/layer/WebGLPoints.js

@@ -0,0 +1,69 @@
+/**
+ * @module ol/layer/WebGLPoints
+ */
+import VectorLayer from './Vector.js';
+import {assign} from '../obj.js';
+import WebGLPointsLayerRenderer from '../renderer/webgl/PointsLayer.js';
+import {getSymbolFragmentShader, getSymbolVertexShader} from '../webgl/ShaderBuilder.js';
+import {assert} from '../asserts.js';
+
+
+/**
+ * @typedef {Object} Options
+ * @property {import('../style/LiteralStyle.js').LiteralStyle} literalStyle Literal style to apply to the layer features.
+ * @property {string} [className='ol-layer'] A CSS class name to set to the layer element.
+ * @property {number} [opacity=1] Opacity (0, 1).
+ * @property {boolean} [visible=true] Visibility.
+ * @property {import("../extent.js").Extent} [extent] The bounding extent for layer rendering.  The layer will not be
+ * rendered outside of this extent.
+ * @property {number} [zIndex] The z-index for layer rendering.  At rendering time, the layers
+ * will be ordered, first by Z-index and then by position. When `undefined`, a `zIndex` of 0 is assumed
+ * for layers that are added to the map's `layers` collection, or `Infinity` when the layer's `setMap()`
+ * method was used.
+ * @property {number} [minResolution] The minimum resolution (inclusive) at which this layer will be
+ * visible.
+ * @property {number} [maxResolution] The maximum resolution (exclusive) below which this layer will
+ * be visible.
+ * @property {import("../source/Vector.js").default} [source] Source.
+ */
+
+
+/**
+ * @classdesc
+ * Layer optimized for rendering large point datasets.
+ * Note that any property set in the options is set as a {@link module:ol/Object~BaseObject}
+ * property on the layer object; for example, setting `title: 'My Title'` in the
+ * options means that `title` is observable, and has get/set accessors.
+ *
+ * @fires import("../render/Event.js").RenderEvent
+ * @api
+ */
+class WebGLPointsLayer extends VectorLayer {
+  /**
+   * @param {Options} options Options.
+   */
+  constructor(options) {
+    const baseOptions = assign({}, options);
+
+    super(baseOptions);
+
+    /**
+     * @type {import('../style/LiteralStyle.js').LiteralStyle}
+     */
+    this.literalStyle = options.literalStyle;
+
+    assert(this.literalStyle.symbol !== undefined, 65);
+  }
+
+  /**
+   * @inheritDoc
+   */
+  createRenderer() {
+    return new WebGLPointsLayerRenderer(this, {
+      vertexShader: getSymbolVertexShader(this.literalStyle.symbol),
+      fragmentShader: getSymbolFragmentShader()
+    });
+  }
+}
+
+export default WebGLPointsLayer;