Make tile cache smaller and screen size dependant

src/ol/source/TileImage.js

@@ -18,7 +18,7 @@ import {getForProjection as getTileGridForProjection} from '../tilegrid.js';
  * @typedef {Object} Options
  * @property {import("./Source.js").AttributionLike} [attributions] Attributions.
  * @property {boolean} [attributionsCollapsible=true] Attributions are collapsible.
- * @property {number} [cacheSize=2048] Cache size.
+ * @property {number} [cacheSize] Tile cache size. Default is twice as many tiles as a fullscreen map needs.
  * @property {null|string} [crossOrigin] The `crossOrigin` attribute for loaded images.  Note that
  * you must provide a `crossOrigin` value if you want to access pixel data with the Canvas renderer.
  * See https://developer.mozilla.org/en-US/docs/Web/HTML/CORS_enabled_image for more detail.