[X] Change the default value for xaml-comp

The default value for the xaml-comp processing instruction used to be
false, meaning the a XAML ResourceDictionary without code-behind wasn't
compiled by XamlC unless the <?xaml-comp compile="true" ?> processing
instruction was specified.

From now on, we will compile all XAML-only RD, unless the <?xaml-comp
compile="false" ?> is set.

Thsi will help with performance and trimming

src/Controls/src/SourceGen/CodeBehindGenerator.cs

@@ -295,7 +295,7 @@ static bool TryParseXaml(SourceText text, string uid, Compilation compilation, A
 
 			if (rootClass != null)
 				XmlnsHelper.ParseXmlns(rootClass.Value, out rootType, out rootClrNamespace, out var rootAsm, out var targetPlatform);
-			else if (hasXamlCompilationProcessingInstruction)
+			else if (hasXamlCompilationProcessingInstruction && root.NamespaceURI == XamlParser.MauiUri)
 			{
 				rootClrNamespace = "__XamlGeneratedCode__";
 				rootType = $"__Type{uid}";
@@ -325,13 +325,13 @@ static bool GetXamlCompilationProcessingInstruction(XmlDocument xmlDoc)
 		{
 			var instruction = xmlDoc.SelectSingleNode("processing-instruction('xaml-comp')") as XmlProcessingInstruction;
 			if (instruction == null)
-				return false;
+				return true;
 
 			var parts = instruction.Data.Split(' ', '=');
 			var indexOfCompile = Array.IndexOf(parts, "compile");
 			if (indexOfCompile != -1)
-				return parts[indexOfCompile + 1].Trim('"', '\'').Equals("true", StringComparison.OrdinalIgnoreCase);
-			return false;
+				return !parts[indexOfCompile + 1].Trim('"', '\'').Equals("false", StringComparison.OrdinalIgnoreCase);
+			return true;
 		}
 
 		static IEnumerable<(string name, string type, string accessModifier)> GetNamedFields(XmlNode root, XmlNamespaceManager nsmgr, Compilation compilation, AssemblyCaches caches, CancellationToken cancellationToken)