[Mono.Android] Hide "internal" members of JLO from IDEs (#4583)

Fixes: #4582

`Java.Lang.Object` and `Java.Lang.Throwable` contain various `public`
and `protected` members that are required by our bindings, such as
the `Handle` and `PeerReference` properties.  We cannot make them
`internal` because our bindings need them, but we can make them
"invisible" to users using IDEs by applying the attributes:

  * [`[EditorBrowsable (EditorBrowsableState.Never)]`][0]
  * [`[DebuggerBrowsable (DebuggerBrowsableState.Never)]`][1]

This will prevent them from showing up in IntelliSense and debugger
displays, as they should not be used by users.

Note they are still usable if needed, they simply do not show up in
IntelliSense.  You have to type them out manually.

Intellisense for a class deriving JLO before:

![before](https://user-images.githubusercontent.com/179295/79778416-4fc78000-82fe-11ea-840a-fb0b4688d6aa.png)

After:

![after](https://user-images.githubusercontent.com/179295/79778430-535b0700-82fe-11ea-9ff6-d6e41eabcf9a.png)

[0]: https://docs.microsoft.com/en-us/dotnet/api/system.componentmodel.editorbrowsableattribute
[1]: https://docs.microsoft.com/en-us/dotnet/api/system.diagnostics.debuggerbrowsableattribute

Author: jpobst

Documentation/release-notes/4583.md

@@ -0,0 +1,17 @@
+### Tidier IntelliSense suggestions for Java.Lang.Object subclasses
+
+`Java.Lang.Object` contains several properties and methods that are
+required to be `public` to support bindings, but are not intended
+to be called by users.  Use `[EditorBrowser]` to hide them from
+IntelliSense, making it easier to find useful members.
+
+[IntelliSense cleanup)[images/4583.png]
+
+### Issues fixed
+
+#### IDE compatibility
+
+  * [GitHub 4582](https://github.com/xamarin/xamarin-android/issues/4582):
+    Some `Java.Lang.Object` properties and methods like `Handle` and
+    `PeerReference` appeared in IntelliSense suggestions even though they were
+    primarily intended for use only in generated code.

Documentation/release-notes/images/4583.png

@@ -6,6 +6,8 @@
 using Java.Interop;
 
 using Android.Runtime;
+using System.ComponentModel;
+using System.Diagnostics;
 
 namespace Java.Lang {
 
@@ -91,21 +93,27 @@ internal void SetHandleOnDeserialized (StreamingContext context)
 		}
 
 #if JAVA_INTEROP
+		[EditorBrowsable (EditorBrowsableState.Never)]
 		public int JniIdentityHashCode {
 			get {return (int) key_handle;}
 		}
 
+		[DebuggerBrowsable (DebuggerBrowsableState.Never)]
+		[EditorBrowsable (EditorBrowsableState.Never)]
 		public JniObjectReference PeerReference {
 			get {
 				return new JniObjectReference (handle, (JniObjectReferenceType) handle_type);
 			}
 		}
 
+		[DebuggerBrowsable (DebuggerBrowsableState.Never)]
+		[EditorBrowsable (EditorBrowsableState.Never)]
 		public virtual JniPeerMembers JniPeerMembers {
 			get { return _members; }
 		}
 #endif  // JAVA_INTEROP
 
+		[EditorBrowsable (EditorBrowsableState.Never)]
 		public IntPtr Handle {
 			get {
 				if (weak_handle != IntPtr.Zero)
@@ -115,10 +123,14 @@ public IntPtr Handle {
 			}
 		}
 
+		[DebuggerBrowsable (DebuggerBrowsableState.Never)]
+		[EditorBrowsable (EditorBrowsableState.Never)]
 		protected virtual IntPtr ThresholdClass {
 			get { return Class.Object; }
 		}
 
+		[DebuggerBrowsable (DebuggerBrowsableState.Never)]
+		[EditorBrowsable (EditorBrowsableState.Never)]
 		protected virtual System.Type ThresholdType {
 			get { return typeof (Java.Lang.Object); }
 		}
@@ -154,6 +166,7 @@ void IJavaPeerable.DisposeUnlessReferenced ()
 			}
 		}
 
+		[EditorBrowsable (EditorBrowsableState.Never)]
 		public void UnregisterFromRuntime ()
 		{
 			JNIEnv.AndroidValueManager.RemovePeer (this, key_handle);
@@ -231,6 +244,7 @@ internal static void Dispose (IJavaPeerable instance, ref IntPtr handle, IntPtr
 			}
 		}
 
+		[EditorBrowsable (EditorBrowsableState.Never)]
 		protected void SetHandle (IntPtr value, JniHandleOwnership transfer)
 		{
 			JNIEnv.AndroidValueManager.AddPeer (this, value, transfer, out handle);
@@ -287,6 +301,7 @@ internal static IJavaPeerable GetObject (IntPtr handle, JniHandleOwnership trans
 			return Java.Interop.TypeManager.CreateInstance (handle, transfer, type);
 		}
 
+		[EditorBrowsable (EditorBrowsableState.Never)]
 		public T[] ToArray<T>()
 		{
 			return JNIEnv.GetArray<T>(Handle);

src/Mono.Android/Java.Lang/Object.cs

@@ -4,6 +4,8 @@
 using Java.Interop;
 
 using Android.Runtime;
+using System.ComponentModel;
+using System.Diagnostics;
 
 namespace Java.Lang {
 
@@ -171,27 +173,37 @@ public override string ToString ()
 		}
 
 #if JAVA_INTEROP
+		[EditorBrowsable (EditorBrowsableState.Never)]
 		public int JniIdentityHashCode {
 			get {return (int) key_handle;}
 		}
 
+		[DebuggerBrowsable (DebuggerBrowsableState.Never)]
+		[EditorBrowsable (EditorBrowsableState.Never)]
 		public JniObjectReference PeerReference {
 			get {
 				return new JniObjectReference (handle, (JniObjectReferenceType) handle_type);
 			}
 		}
 
+		[DebuggerBrowsable (DebuggerBrowsableState.Never)]
+		[EditorBrowsable (EditorBrowsableState.Never)]
 		public virtual JniPeerMembers JniPeerMembers {
 			get { return _members; }
 		}
 #endif  // JAVA_INTEROP
 
+		[EditorBrowsable (EditorBrowsableState.Never)]
 		public IntPtr Handle { get { return handle; } }
 
+		[DebuggerBrowsable (DebuggerBrowsableState.Never)]
+		[EditorBrowsable (EditorBrowsableState.Never)]
 		protected virtual IntPtr ThresholdClass {
 			get { return class_ref; }
 		}
 
+		[DebuggerBrowsable (DebuggerBrowsableState.Never)]
+		[EditorBrowsable (EditorBrowsableState.Never)]
 		protected virtual System.Type ThresholdType {
 			get { return typeof (Java.Lang.Throwable); }
 		}
@@ -226,6 +238,7 @@ public unsafe Java.Lang.Class Class {
 			}
 		}
 
+		[EditorBrowsable (EditorBrowsableState.Never)]
 		protected void SetHandle (IntPtr value, JniHandleOwnership transfer)
 		{
 			JNIEnv.AndroidValueManager.AddPeer (this, value, transfer, out handle);