[coretext] Use [MarshalAs (UnmanagedType.I1)] on `bool` parameters used with native code. Fixes #52162

iOS 10.3 simulator (i386 only) will crash executing CTLineTests.
EnumerateCaretOffsets test case. This was not a problem with older SDK
so the code likely changed (but the issue was in our code)

src/CoreText/CTLine.cs

@@ -233,7 +233,7 @@ namespace XamCore.CoreText {
 		}
 
 		public delegate void CaretEdgeEnumerator (double offset, nint charIndex, bool leadingEdge, ref bool stop);
-		unsafe delegate void CaretEdgeEnumeratorProxy (IntPtr block, double offset, nint charIndex, bool leadingEdge, ref bool stop);
+		unsafe delegate void CaretEdgeEnumeratorProxy (IntPtr block, double offset, nint charIndex, [MarshalAs (UnmanagedType.I1)] bool leadingEdge, [MarshalAs (UnmanagedType.I1)] ref bool stop);
 		
 		[iOS (9,0)][Mac (10,11)]
 		[DllImport (Constants.CoreTextLibrary)]