Add platform image encoder for using NDK APIs

Bug: skia:10369

Add SkEncodeImageWithNDK, mirroring the CG and WIC versions, for
encoding with the NDK APIs added to R.

Rename SK_ENABLE_NDK_DECODING to SK_ENABLE_NDK_IMAGES and use it for
both encoding and decoding.

Move code for converting to/from NDK types into a common location.

Update encode_platform.cpp to use NDK encoding APIs when available and
to use both types of webp (lossy and lossless). Add tests specifically
for the new implementation.

Update NdkDecodeTest to use ToolUtils::equal_pixels for comparing
pixels.

Change-Id: Ic62f89af27372ccce90b8e028e01c388a135a68c
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/308800
Commit-Queue: Leon Scroggins <scroggo@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
diff --git a/RELEASE_NOTES.txt b/RELEASE_NOTES.txt
index 259e330..4ebaa87 100644
--- a/RELEASE_NOTES.txt
+++ b/RELEASE_NOTES.txt
@@ -11,8 +11,10 @@
     as 'uniforms'.
     https://review.skia.org/309050
 
-  * Add SkImageGeneratorNDK for using Android's NDK APIs to decode.
-    https://review.skia.org/305689
+  * Add SkImageGeneratorNDK and SkEncodeImageWithNDK for using Android's NDK APIs to decode and
+    encode.
+    https://review.skia.org/308185
+    https://review.skia.org/308800
 
   * SkImage:remove DecodeToRaster, DecodeToTexture
     https://review.skia.org/306331