Add JimpMime constant (#1331)

Author: hipstersmoothie

packages/docs/src/content/docs/guides/migrate-to-v1.mdx

@@ -147,7 +147,17 @@ const resized = await image
 ## Removed Constants
 
 - `Jimp.AUTO` - This constant was only needed for positional arguments. It is no longer needed with the new API.
-- `Jimp.MIME_*` - These are now part of the TS api when encoding
+
+### `Jimp.MIME_*`
+
+These have moved to a named export `JimpMime`.
+
+```js
+import { JimpMime } from "jimp";
+
+JimpMime.jpeg;
+```
+
 
 ## Moved Functions
 

packages/jimp/src/index.ts

@@ -54,6 +54,15 @@ export const defaultPlugins = [
 
 export const defaultFormats = [bmp, msBmp, gif, jpeg, png, tiff];
 
+/** Convenience object for getting the MIME types of the default formats */
+export const JimpMime = {
+  bmp: bmp().mime,
+  gif: gif().mime,
+  jpeg: jpeg().mime,
+  png: png().mime,
+  tiff: tiff().mime,
+};
+
 // TODO: This doesn't document the constructor of the class
 /**
  * @class