[impeller] use lossy texture compression on iOS (#40520)

[Impeller] use lossy texture compression on iOS for decode images and MSAA resolve textures.

impeller/renderer/render_target.cc

diff --git a/impeller/renderer/render_target.cc b/impeller/renderer/render_target.cc
index aba17fd..64304f3 100644
--- a/impeller/renderer/render_target.cc
+++ b/impeller/renderer/render_target.cc
@@ -297,6 +297,7 @@
       color_attachment_config.resolve_storage_mode;
   color0_resolve_tex_desc.format = pixel_format;
   color0_resolve_tex_desc.size = size;
+  color0_resolve_tex_desc.compression_type = CompressionType::kLossy;
   color0_resolve_tex_desc.usage =
       static_cast<uint64_t>(TextureUsage::kRenderTarget) |
       static_cast<uint64_t>(TextureUsage::kShaderRead);

lib/ui/painting/image_decoder_impeller.cc

diff --git a/lib/ui/painting/image_decoder_impeller.cc b/lib/ui/painting/image_decoder_impeller.cc
index 51a651f..223cff5 100644
--- a/lib/ui/painting/image_decoder_impeller.cc
+++ b/lib/ui/painting/image_decoder_impeller.cc
@@ -269,6 +269,7 @@
   texture_descriptor.format = pixel_format.value();
   texture_descriptor.size = {image_info.width(), image_info.height()};
   texture_descriptor.mip_count = texture_descriptor.size.MipCount();
+  texture_descriptor.compression_type = impeller::CompressionType::kLossy;
 
   auto dest_texture =
       context->GetResourceAllocator()->CreateTexture(texture_descriptor);