Add alignment padding to floats in std codec (#3780)

shell/platform/darwin/ios/framework/Source/FlutterStandardCodec.mm

@@ -275,6 +275,7 @@ using namespace shell;
     } else if (strcmp(type, @encode(double)) == 0 || strcmp(type, @encode(float)) == 0) {
       Float64 f = number.doubleValue;
       [self writeByte:FlutterStandardFieldFloat64];
+      [self writeAlignment:8];
       [_data appendBytes:(UInt8*)&f length:8];
     } else if (strcmp(type, @encode(unsigned long)) == 0 ||
                strcmp(type, @encode(signed long long)) == 0 ||
@@ -430,6 +431,7 @@ using namespace shell;
     }
     case FlutterStandardFieldFloat64: {
       Float64 value;
+      [self readAlignment:8];
       [self readBytes:&value length:8];
       return [NSNumber numberWithDouble:value];
     }

shell/platform/darwin/ios/framework/Source/flutter_standard_codec_unittest.mm

@@ -103,13 +103,13 @@ TEST(FlutterStandardCodec, CanEncodeAndDecodeBigInteger) {
 }
 
 TEST(FlutterStandardCodec, CanEncodeAndDecodeFloat32) {
-  char bytes[9] = {0x06, 0x00, 0x00, 0x00, 0x60, 0xfb, 0x21, 0x09, 0x40};
-  checkEncodeDecode(@3.1415927f, [NSData dataWithBytes:bytes length:9]);
+  char bytes[16] = {0x06, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x60, 0xfb, 0x21, 0x09, 0x40};
+  checkEncodeDecode(@3.1415927f, [NSData dataWithBytes:bytes length:16]);
 }
 
 TEST(FlutterStandardCodec, CanEncodeAndDecodeFloat64) {
-  char bytes[9] = {0x06, 0x18, 0x2d, 0x44, 0x54, 0xfb, 0x21, 0x09, 0x40};
-  checkEncodeDecode(@3.14159265358979311599796346854, [NSData dataWithBytes:bytes length:9]);
+  char bytes[16] = {0x06, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x18, 0x2d, 0x44, 0x54, 0xfb, 0x21, 0x09, 0x40};
+  checkEncodeDecode(@3.14159265358979311599796346854, [NSData dataWithBytes:bytes length:16]);
 }
 
 TEST(FlutterStandardCodec, CanEncodeAndDecodeString) {