Add documentation for Java interop types. (#120964)

Fixes #120504

Author: AaronRobinsonMSFT

src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Java/ComponentCrossReference.cs

@@ -5,6 +5,9 @@
 
 namespace System.Runtime.InteropServices.Java
 {
+    /// <summary>
+    /// Represents a cross-reference between two tracked component groups.
+    /// </summary>
     [CLSCompliant(false)]
     [SupportedOSPlatform("android")]
     [StructLayout(LayoutKind.Sequential)]

src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Java/MarkCrossReferencesArgs.cs

@@ -5,14 +5,33 @@
 
 namespace System.Runtime.InteropServices.Java
 {
+    /// <summary>
+    /// Data for the callback supplied to <see cref="O:JavaMarshal.Initialize" />
+    /// for marking managed objects referenced from Java during cross-reference processing.
+    /// </summary>
     [CLSCompliant(false)]
     [SupportedOSPlatform("android")]
     [StructLayout(LayoutKind.Sequential)]
     public unsafe struct MarkCrossReferencesArgs
     {
+        /// <summary>
+        /// The number of strongly connected components being reported.
+        /// </summary>
         public nuint ComponentCount;
+
+        /// <summary>
+        /// A pointer to the array of strongly connected components.
+        /// </summary>
         public StronglyConnectedComponent* Components;
+
+        /// <summary>
+        /// The number of cross-references being reported.
+        /// </summary>
         public nuint CrossReferenceCount;
+
+        /// <summary>
+        /// A pointer to the array of cross-references.
+        /// </summary>
         public ComponentCrossReference* CrossReferences;
     }
 }

src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Java/StronglyConnectedComponent.cs

@@ -5,6 +5,10 @@
 
 namespace System.Runtime.InteropServices.Java
 {
+    /// <summary>
+    /// Represents a strongly connected component of managed objects
+    /// referenced for cross-reference processing.
+    /// </summary>
     [CLSCompliant(false)]
     [SupportedOSPlatform("android")]
     [StructLayout(LayoutKind.Sequential)]