Add Transform2d::Inverse() (#2407)

This is useful for undoing transformations. One application my FRC team
found was converting perspective n-point data from a "camera to target"
coordinate frame transformation to a "target to camera" coordinate frame
transformation.

wpilibc/src/main/native/include/frc/geometry/Transform2d.h

@@ -1,5 +1,5 @@
 /*----------------------------------------------------------------------------*/
-/* Copyright (c) 2019 FIRST. All Rights Reserved.                             */
+/* Copyright (c) 2019-2020 FIRST. All Rights Reserved.                        */
 /* Open Source Software - may be modified and shared by FRC teams. The code   */
 /* must be accompanied by the FIRST BSD license file in the root directory of */
 /* the project.                                                               */
@@ -53,6 +53,13 @@ class Transform2d {
    */
   const Rotation2d& Rotation() const { return m_rotation; }
 
+  /**
+   * Invert the transformation. This is useful for undoing a transformation.
+   *
+   * @return The inverted transformation.
+   */
+  Transform2d Inverse() const;
+
   /**
    * Scales the transform by the scalar.
    *