[wpilib] Make protected fields in accelerometers/gyros private (#6134)

This avoids needing add redundant JavaDocs to them, and better reflects
how we design our modern classes (the classes modified here were around
with minimal changes since 2008 or so).

wpilibc/src/main/native/include/frc/AnalogGyro.h

@@ -218,10 +218,8 @@ class AnalogGyro : public wpi::Sendable,
 
   void InitSendable(wpi::SendableBuilder& builder) override;
 
- protected:
-  std::shared_ptr<AnalogInput> m_analog;
-
  private:
+  std::shared_ptr<AnalogInput> m_analog;
   hal::Handle<HAL_GyroHandle> m_gyroHandle;
 };