Support zoom limits for layers

examples/layer-zoom-limits.html

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+---
+layout: example.html
+title: Layer Zoom Limits
+shortdesc: Using minZoom and maxZoom to control layer visibility.
+docs: >
+  Layers support `minZoom` and `maxZoom` options for controlling visibility based on the view's zoom level.
+  If min or max zoom are set, the layer will only be visible at zoom levels greater than the `minZoom` and
+  less than or equal to the `maxZoom`.  After construction, the layer's `setMinZoom` and `setMaxZoom` can
+  be used to set limits.  This example shows an OSM layer at zoom levels 14 and lower and a USGS layer at
+  zoom levels higher than 14.
+tags: "minZoom, maxZoom, layer"
+---
+<div id="map" class="map"></div>

examples/layer-zoom-limits.js

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+import Map from '../src/ol/Map.js';
+import View from '../src/ol/View.js';
+import TileLayer from '../src/ol/layer/Tile.js';
+import OSM from '../src/ol/source/OSM.js';
+import XYZ from '../src/ol/source/XYZ.js';
+import {transformExtent, fromLonLat} from '../src/ol/proj.js';
+
+const mapExtent = [-112.261791, 35.983744, -112.113981, 36.132062];
+
+const map = new Map({
+  target: 'map',
+  layers: [
+    new TileLayer({
+      maxZoom: 14, // visible at zoom levels 14 and below
+      source: new OSM()
+    }),
+    new TileLayer({
+      minZoom: 14, // visible at zoom levels above 14
+      source: new XYZ({
+        attributions: 'Tiles © USGS, rendered with ' +
+        '<a href="http://www.maptiler.com/">MapTiler</a>',
+        url: 'https://tileserver.maptiler.com/grandcanyon/{z}/{x}/{y}.png'
+      })
+    })
+  ],
+  view: new View({
+    center: fromLonLat([-112.18688965, 36.057944835]),
+    zoom: 15,
+    maxZoom: 18,
+    extent: transformExtent(mapExtent, 'EPSG:4326', 'EPSG:3857'),
+    constrainOnlyCenter: true
+  })
+});