[wpilibc] Try to work around ABI break introduced in #2901 (#2917)

The change to SendableBuilder to add GetTable() added a virtual function
early in the class definition.  This is an ABI break for vendor libraries.
Attempt to workaround this breakage by moving GetTable() to the end of the
class definition.

wpilibc/src/main/native/include/frc/smartdashboard/SendableBuilder.h

@@ -25,12 +25,6 @@ class SendableBuilder {
  public:
   virtual ~SendableBuilder() = default;
 
-  /**
-   * Get the network table.
-   * @return The network table
-   */
-  virtual std::shared_ptr<nt::NetworkTable> GetTable() = 0;
-
   /**
    * Set the string representation of the named data type that will be used
    * by the smart dashboard for this sendable.
@@ -224,6 +218,12 @@ class SendableBuilder {
       const wpi::Twine& key,
       std::function<wpi::StringRef(wpi::SmallVectorImpl<char>& buf)> getter,
       std::function<void(wpi::StringRef)> setter) = 0;
+
+  /**
+   * Get the network table.
+   * @return The network table
+   */
+  virtual std::shared_ptr<nt::NetworkTable> GetTable() = 0;
 };
 
 }  // namespace frc