Ensure consistent optionality for options.projection for all ImageSource-derived constructor options

src/ol/source/ImageCanvas.js

@@ -33,7 +33,7 @@ import ImageSource from './Image.js';
  * the value returned by the function is later changed then
  * `changed` should be called on the source for the source to
  * invalidate the current cached image. See: {@link module:ol/Observable~Observable#changed}
- * @property {import("../proj.js").ProjectionLike} projection Projection.
+ * @property {import("../proj.js").ProjectionLike} [projection] Projection. Default is the view projection.
  * @property {number} [ratio=1.5] Ratio. 1 means canvases are the size of the map viewport, 2 means twice the
  * width and height of the map viewport, and so on. Must be `1` or higher.
  * @property {Array<number>} [resolutions] Resolutions.

src/ol/source/ImageMapGuide.js

@@ -20,7 +20,7 @@ import {appendParams} from '../uri.js';
  * @property {boolean} [hidpi=true] Use the `ol/Map#pixelRatio` value when requesting
  * the image from the remote server.
  * @property {boolean} [useOverlay] If `true`, will use `GETDYNAMICMAPOVERLAYIMAGE`.
- * @property {import("../proj.js").ProjectionLike} projection Projection.
+ * @property {import("../proj.js").ProjectionLike} [projection] Projection. Default is the view projection.
  * @property {number} [ratio=1] Ratio. `1` means image requests are the size of the map viewport, `2` means
  * twice the width and height of the map viewport, and so on. Must be `1` or higher.
  * @property {Array<number>} [resolutions] Resolutions.

src/ol/source/ImageStatic.js

@@ -19,7 +19,7 @@ import ImageSource, {defaultImageLoadFunction} from './Image.js';
  * @property {import("../extent.js").Extent} [imageExtent] Extent of the image in map coordinates.
  * This is the [left, bottom, right, top] map coordinates of your image.
  * @property {import("../Image.js").LoadFunction} [imageLoadFunction] Optional function to load an image given a URL.
- * @property {import("../proj.js").ProjectionLike} projection Projection.
+ * @property {import("../proj.js").ProjectionLike} [projection] Projection. Default is the view projection.
  * @property {import("../size.js").Size} [imageSize] Size of the image in pixels. Usually the image size is auto-detected, so this
  * only needs to be set if auto-detection fails for some reason.
  * @property {string} url Image URL.