add kRGBA_F16_SkColorType

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1666343002

Review URL: https://codereview.chromium.org/1666343002
diff --git a/include/core/SkImageInfo.h b/include/core/SkImageInfo.h
index 4b82ae6..b2dda3f 100644
--- a/include/core/SkImageInfo.h
+++ b/include/core/SkImageInfo.h
@@ -73,8 +73,9 @@
     kBGRA_8888_SkColorType,
     kIndex_8_SkColorType,
     kGray_8_SkColorType,
+    kRGBA_F16_SkColorType,
 
-    kLastEnum_SkColorType = kGray_8_SkColorType,
+    kLastEnum_SkColorType = kRGBA_F16_SkColorType,
 
 #if SK_PMCOLOR_BYTE_ORDER(B,G,R,A)
     kN32_SkColorType = kBGRA_8888_SkColorType,
@@ -95,6 +96,7 @@
         4,  // BGRA_8888
         1,  // kIndex_8
         1,  // kGray_8
+        8,  // kRGBA_F16
     };
     static_assert(SK_ARRAY_COUNT(gSize) == (size_t)(kLastEnum_SkColorType + 1),
                   "size_mismatch_with_SkColorType_enum");
@@ -114,6 +116,7 @@
 static inline size_t SkColorTypeComputeOffset(SkColorType ct, int x, int y, size_t rowBytes) {
     int shift = 0;
     switch (SkColorTypeBytesPerPixel(ct)) {
+        case 8: shift = 3; break;
         case 4: shift = 2; break;
         case 2: shift = 1; break;
         case 1: shift = 0; break;