Added new I2cController and related support (#505)

* Added new I2cController and related support

* Add bus ID as part of way to manage devices

* Made static

* Removed static

* Removed interop file and add partial class for controller

* Changed to open/close device methods

* Added TryGetDevice method

* Added ShouldDispose property

* Added more support for disposing

* Enabled nullable in file to check builds

* Missed the other file for enabling nullable

* Added GetDevices and updated OpenDevice check

* Updated to ConcurrentDictionary

* Consolidated to only Create I2cDevice

* Removed unused files

* Removed until direction is determined

* Moved Create under I2cDevice classes

src/System.Device.Gpio/System/Device/I2c/I2cDevice.Linux.cs

+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+namespace System.Device.I2c
+{
+    public partial class I2cDevice
+    {
+        /// <summary>
+        /// Creates a communications channel to a device on an I2C bus running on Unix.
+        /// </summary>
+        /// <param name="settings">The connection settings of a device on an I2C bus.</param>
+        /// <returns>A communications channel to a device on an I2C bus running on Unix.</returns>
+        public static I2cDevice Create(I2cConnectionSettings settings) => new Drivers.UnixI2cDevice(settings);
+    }
+}

src/System.Device.Gpio/System/Device/I2c/I2cDevice.Windows.cs

+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+namespace System.Device.I2c
+{
+    public partial class I2cDevice
+    {
+        /// <summary>
+        /// Creates a communications channel to a device on an I2C bus running on Windows 10 IoT.
+        /// </summary>
+        /// <param name="settings">The connection settings of a device on an I2C bus.</param>
+        /// <returns>A communications channel to a device on an I2C bus running on Windows 10 IoT.</returns>
+        public static I2cDevice Create(I2cConnectionSettings settings) => new Drivers.Windows10I2cDevice(settings);
+    }
+}

src/System.Device.Gpio/System/Device/I2c/I2cDevice.cs

@@ -7,7 +7,7 @@ namespace System.Device.I2c
     /// <summary>
     /// The communications channel to a device on an I2C bus.
     /// </summary>
-    public abstract class I2cDevice : IDisposable
+    public abstract partial class I2cDevice : IDisposable
     {
         /// <summary>
         /// The connection settings of a device on an I2C bus.