New MEDIASUBTYPE_ guid constants are faulty

[AArnott]

In updating CsWin32 to the latest metadata (29.0.6), we hit a snag that blocks adoption. Some new guid constants are included in the metadata that are causing us trouble:

  Message: 
Microsoft.Windows.CsWin32.GenerationFailedException : Failed creating field: Windows.Win32.Media.MediaFoundation.Apis.MEDIASUBTYPE_P208
---- System.BadImageFormatException : Read out of bounds.

  Stack Trace: 
Generator.DeclareConstant(FieldDefinition fieldDef) line 3192
<>c__DisplayClass165_0.<RequestConstant>b__0() line 1494
GeneratedCode.GenerateConstant(FieldDefinitionHandle fieldDefinitionHandle, Action generator) line 6090
Generator.RequestConstant(FieldDefinitionHandle fieldDefHandle) line 1491
<>c__DisplayClass137_0.<GenerateAllConstants>b__1() line 756
GeneratedCode.GenerationTransaction(Action generator) line 5988
Generator.GenerateAllConstants(CancellationToken cancellationToken) line 754
Generator.GenerateAll(CancellationToken cancellationToken) line 573
GeneratorTests.FullGeneration(MarshalingOptions marshaling, Boolean useIntPtrForComOutPtr, Platform platform) line 1549
----- Inner Stack Trace -----
Throw.OutOfBounds()
CustomAttributeDecoder`1.DecodeArgument(BlobReader& valueReader, ArgumentTypeInfo info)
CustomAttributeDecoder`1.DecodeFixedArguments(BlobReader& signatureReader, BlobReader& valueReader, Int32 count)
CustomAttributeDecoder`1.DecodeValue(EntityHandle constructor, BlobHandle value)
CustomAttribute.DecodeValue[TType](ICustomAttributeTypeProvider`1 provider)
Generator.GuidValue(CustomAttribute guidAttribute) line 2335
Generator.DeclareConstant(FieldDefinition fieldDef) line 3135

Looking at the metadata, I see the constant is defined like this:

.field public static valuetype [netstandard]System.Guid MEDIASUBTYPE_P208
.custom instance void [Windows.Win32.Interop]Windows.Win32.Interop.GuidAttribute::.ctor(uint32, uint16, uint16, uint8, uint8, uint8, uint8, uint8, uint8, uint8, uint8) = (
	01 00 00 00 10 00 80 00 00 aa 00 38 9b 71 00 00
)

But this is inconsistent with other Guid constants that do work, like this one:

.field public static valuetype [netstandard]System.Guid WIA_CATEGORY_FINISHED_FILE
.custom instance void [Windows.Win32.Interop]Windows.Win32.Interop.GuidAttribute::.ctor(uint32, uint16, uint16, uint8, uint8, uint8, uint8, uint8, uint8, uint8, uint8) = (
	01 00 ca 77 2b ff 84 cf 2b 43 a7 35 3a 13 0d de
	2a 88 00 00
)

Note how there are 4 bytes missing from the broken guid constant.

[AArnott]

Duplicate of #1116