Add constants for built-in Shuffleboard widgets and layouts (#1468)

Prevents users from having to remember (and correctly type) the names of Shuffleboard widgets.

wpilibc/src/main/native/include/frc/shuffleboard/BuiltInLayouts.h

@@ -0,0 +1,53 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2018 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.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#pragma once
+
+#include "frc/shuffleboard/LayoutType.h"
+
+namespace frc {
+
+/**
+ * The types of layouts bundled with Shuffleboard.
+ *
+ * <pre>{@code
+ * ShuffleboardLayout myList = Shuffleboard::GetTab("My Tab")
+ *   .GetLayout(BuiltinLayouts::kList, "My List");
+ * }</pre>
+ */
+class BuiltInLayouts {
+ public:
+  /**
+   * Groups components in a vertical list. New widgets added to the layout will
+   * be placed at the bottom of the list. <br>Custom properties: <table>
+   * <tr><th>Name</th><th>Type</th><th>Default Value</th><th>Notes</th></tr>
+   * <tr><td>Label position</td><td>String</td><td>"BOTTOM"</td>
+   * <td>The position of component labels inside the grid. One of
+   * {@code ["TOP", "LEFT", "BOTTOM", "RIGHT", "HIDDEN"}</td></tr>
+   * </table>
+   */
+  static const LayoutType kList;
+
+  /**
+   * Groups components in an <i>n</i> x <i>m</i> grid. Grid layouts default to
+   * 3x3. <br>Custom properties: <table>
+   * <tr><th>Name</th><th>Type</th><th>Default Value</th><th>Notes</th></tr>
+   * <tr><td>Number of columns</td><td>Number</td><td>3</td><td>Must be in the
+   * range [1,15]</td>
+   * </tr>
+   * <tr><td>Number of rows</td><td>Number</td><td>3</td><td>Must be in the
+   * range [1,15]</td></tr> <tr> <td>Label position</td> <td>String</td>
+   * <td>"BOTTOM"</td>
+   * <td>The position of component labels inside the grid.
+   * One of {@code ["TOP", "LEFT", "BOTTOM", "RIGHT", "HIDDEN"}</td>
+   * </tr>
+   * </table>
+   */
+  static const LayoutType kGrid;
+};
+
+}  // namespace frc