Add Magic Kernel Sharp (no relation) to resizing kernels

lib/index.d.ts

@@ -1729,6 +1729,8 @@ declare namespace sharp {
         mitchell: 'mitchell';
         lanczos2: 'lanczos2';
         lanczos3: 'lanczos3';
+        mks2013: 'mks2013';
+        mks2021: 'mks2021';
     }
 
     interface PresetEnum {

lib/resize.js

@@ -150,6 +150,8 @@ function isResizeExpected (options) {
  * - `mitchell`: Use a [Mitchell-Netravali spline](https://www.cs.utexas.edu/~fussell/courses/cs384g-fall2013/lectures/mitchell/Mitchell.pdf).
  * - `lanczos2`: Use a [Lanczos kernel](https://en.wikipedia.org/wiki/Lanczos_resampling#Lanczos_kernel) with `a=2`.
  * - `lanczos3`: Use a Lanczos kernel with `a=3` (the default).
+ * - `mks2013`: Use a [Magic Kernel Sharp](https://johncostella.com/magic/mks.pdf) 2013 kernel, as adopted by Facebook.
+ * - `mks2021`: Use a Magic Kernel Sharp 2021 kernel, with more accurate (reduced) sharpening than the 2013 version.
  *
  * When upsampling, these kernels map to `nearest`, `linear` and `cubic` interpolators.
  * Downsampling kernels without a matching upsampling interpolator map to `cubic`.