Create mipmaps for images when uploading them on the IO thread (#7751)

This does several things:
- It adds CPU time on the IO thread, but avoids GPU time on the GPU
  thread.
- For images that are never drawn with mipmaps, it adds about 33%
  memory overhead. For images that are drawn with mipmaps, it saves
  an entire copy of the base level.
- It fixes https://github.com/flutter/flutter/issues/24517, which is
  a driver bug related to mip-mapping and cross-context images.

Overall, I think the tradeoff is good, but I'm curious to see what
benchmarks look like.

lib/ui/painting/codec.cc

@@ -70,7 +70,7 @@ static sk_sp<SkImage> DecodeImage(fml::WeakPtr<GrContext> context,
     // This indicates that we do not want a "linear blending" decode.
     sk_sp<SkColorSpace> dstColorSpace = nullptr;
     return SkImage::MakeCrossContextFromEncoded(
-        context.get(), std::move(buffer), false, dstColorSpace.get(), true);
+        context.get(), std::move(buffer), true, dstColorSpace.get(), true);
   } else {
     // Defer decoding until time of draw later on the GPU thread. Can happen
     // when GL operations are currently forbidden such as in the background
@@ -131,7 +131,7 @@ fml::RefPtr<Codec> InitCodecUncompressed(
   sk_sp<SkImage> skImage;
   if (context) {
     SkPixmap pixmap(image_info.sk_info, buffer->data(), image_info.row_bytes);
-    skImage = SkImage::MakeCrossContextFromPixmap(context.get(), pixmap, false,
+    skImage = SkImage::MakeCrossContextFromPixmap(context.get(), pixmap, true,
                                                   nullptr, true);
   } else {
     skImage = SkImage::MakeRasterData(image_info.sk_info, std::move(buffer),
@@ -455,7 +455,7 @@ sk_sp<SkImage> MultiFrameCodec::GetNextFrameImage(
     // This indicates that we do not want a "linear blending" decode.
     sk_sp<SkColorSpace> dstColorSpace = nullptr;
     return SkImage::MakeCrossContextFromPixmap(resourceContext.get(), pixmap,
-                                               false, dstColorSpace.get());
+                                               true, dstColorSpace.get());
   } else {
     // Defer decoding until time of draw later on the GPU thread. Can happen
     // when GL operations are currently forbidden such as in the background