CSHARP-4895: Mark API as obsolete: Driver + Core (#1500)

src/MongoDB.Driver/MongoClientBase.cs

@@ -25,6 +25,7 @@ namespace MongoDB.Driver
     /// <summary>
     /// Base class for implementors of <see cref="IMongoClient"/>.
     /// </summary>
+    [Obsolete("This class will be removed in a later release.")]
     public abstract class MongoClientBase : IMongoClient
     {
         /// <inheritdoc />

src/MongoDB.Driver/MongoCollectionBase.cs

@@ -29,6 +29,7 @@ namespace MongoDB.Driver
     /// Base class for implementors of <see cref="IMongoCollection{TDocument}"/>.
     /// </summary>
     /// <typeparam name="TDocument">The type of the document.</typeparam>
+    [Obsolete("This class will be made internal in a later release.")]
     public abstract class MongoCollectionBase<TDocument> : IMongoCollection<TDocument>
     {
         /// <inheritdoc />

src/MongoDB.Driver/MongoDatabaseBase.cs

@@ -23,6 +23,7 @@ namespace MongoDB.Driver
     /// <summary>
     /// Base class for implementors of <see cref="IMongoDatabase" />.
     /// </summary>
+    [Obsolete("This class will be removed in a later release.")]
     public abstract class MongoDatabaseBase : IMongoDatabase
     {
         // public properties

tests/MongoDB.Driver.TestConsoleApplication/MongoDB.Driver.TestConsoleApplication.csproj

@@ -22,7 +22,8 @@
       CA1801;
       CA1812;
       CA1822;
-      CA2007
+      CA2007;
+      CS0618
     </NoWarn>
   </PropertyGroup>