Remove Type caches in DataContractSerialization

[eerhardt]

In DataContractSerialization we have a few places where we are caching typeof(XX) into static Type variables. For example:

runtime/src/libraries/System.Private.DataContractSerialization/src/System/Runtime/Serialization/Globals.cs

Lines 47 to 78 in 855e296

	private static Type? s_typeOfObject;
	internal static Type TypeOfObject
	{
	get
	{
	if (s_typeOfObject == null)
	s_typeOfObject = typeof(object);
	return s_typeOfObject;
	}
	}
	private static Type? s_typeOfValueType;
	internal static Type TypeOfValueType
	{
	get
	{
	if (s_typeOfValueType == null)
	s_typeOfValueType = typeof(ValueType);
	return s_typeOfValueType;
	}
	}
	private static Type? s_typeOfArray;
	internal static Type TypeOfArray
	{
	get
	{
	if (s_typeOfArray == null)
	s_typeOfArray = typeof(Array);
	return s_typeOfArray;
	}
	}

We should remove these caches, where possible, and instead just use typeof(XX) directly inline as needed. This will allow the JIT to see that the code is using runtime Type instances, and it can optimize the code if possible.

See #42824 (comment).

[eerhardt]

Also consider addressing this PR comment as well: #42911 (comment)

but could we specify the parameter types in the GetMethod call?

Fully qualify the parameter types when using Reflection to find methods.