Webgl layer / remove @api tag & better doc

Also the webgl layer now only inherits from the Layer class,
not the VectorLayer one.

src/ol/style/LiteralStyle.js

@@ -5,29 +5,6 @@
  */
 
 /**
- * Here are a few samples of literal style objects:
- * ```js
- * const style = {
- *   symbol: {
- *     symbolType: 'circle',
- *     size: 8,
- *     color: '#33AAFF',
- *     opacity: 0.9
- *   }
- * }
- * ```
- *
- * ```js
- * const style = {
- *   symbol: {
- *     symbolType: 'image',
- *     offset: [0, 12],
- *     size: [4, 8],
- *     src: '../static/exclamation-mark.png'
- *   }
- * }
- * ```
- *
  * @typedef {Object} LiteralStyle
  * @property {LiteralSymbolStyle} [symbol] Symbol representation.
  */
@@ -49,7 +26,7 @@ export const SymbolType = {
  * @property {SymbolType} symbolType Symbol type to use, either a regular shape or an image.
  * @property {string} [src] Path to the image to be used for the symbol. Only required with `symbolType: 'image'`.
  * @property {import("../color.js").Color|string} [color='#FFFFFF'] Color used for the representation (either fill, line or symbol).
- * @property {number} [opacity=0] Opacity.
+ * @property {number} [opacity=1] Opacity.
  * @property {Array.<number, number>} [offset] Offset on X and Y axis for symbols. If not specified, the symbol will be centered.
  * @property {Array.<number, number, number, number>} [textureCoord] Texture coordinates. If not specified, the whole texture will be used (range for 0 to 1 on both axes).
  * @property {boolean} [rotateWithView=false] Specify whether the symbol must rotate with the view or stay upwards.