Remove hidden files from indexer results (#4325)

* Added functionality to not display hidden files

* Added interfaces for seperating db layer

* Updated variable naming and refactored Database connection class

* Added tests for WindowsSearchAPI class

* Fixed nit with braces

* Added function to test that all connections from database are closed

src/modules/launcher/Plugins/Microsoft.Plugin.Indexer/SearchHelper/OleDBSearch.cs

@@ -0,0 +1,80 @@
+using Microsoft.Plugin.Indexer.Interface;
+using System;
+using System.Collections.Generic;
+using System.Data.OleDb;
+
+namespace Microsoft.Plugin.Indexer.SearchHelper
+{
+    public class OleDBSearch : ISearch
+    {
+        private OleDbCommand command;
+        private OleDbConnection conn;
+        private OleDbDataReader WDSResults;
+
+        public List<OleDBResult> Query(string connectionString, string sqlQuery)
+        {
+            List<OleDBResult> result = new List<OleDBResult>();
+
+            using (conn = new OleDbConnection(connectionString))
+            {
+                // open the connection
+                conn.Open();
+
+                // now create an OleDB command object with the query we built above and the connection we just opened.
+                using (command = new OleDbCommand(sqlQuery, conn))
+                {
+                    using (WDSResults = command.ExecuteReader())
+                    {
+                        if (WDSResults.HasRows)
+                        {
+                            while (WDSResults.Read())
+                            {
+                                List<Object> fieldData = new List<object>();
+                                for (int i = 0; i < WDSResults.FieldCount; i++)
+                                {
+                                    fieldData.Add(WDSResults.GetValue(i));
+                                }
+                                result.Add(new OleDBResult(fieldData));
+                            }
+                        }
+                    }
+                }
+            }
+
+            return result;
+        }
+
+        /// Checks if all the variables related to database connection have been properly disposed 
+        public bool HaveAllDisposableItemsBeenDisposed()
+        {
+            bool commandDisposed = false;
+            bool connDisposed = false;
+            bool resultDisposed = false;
+
+            try
+            {
+                command.ExecuteReader();
+            }
+            catch (InvalidOperationException)
+            {
+                commandDisposed = true;
+            }
+
+            try
+            {
+                WDSResults.Read();
+            }
+            catch (InvalidOperationException)
+            {
+                resultDisposed = true;
+            }
+
+            if(conn.State == System.Data.ConnectionState.Closed)
+            {
+                connDisposed = true;
+            }
+
+            return commandDisposed && resultDisposed && connDisposed;
+        }
+    }
+}