[wpilib] Add warning about onboard I2C (#3842)

wpilibj/src/main/java/edu/wpi/first/wpilibj/I2C.java

@@ -43,6 +43,12 @@ public class I2C implements AutoCloseable {
     m_port = port.value;
     m_deviceAddress = deviceAddress;
 
+    if (port == I2C.Port.kOnboard) {
+      DriverStation.reportWarning(
+          "Onboard I2C port is subject to system lockups. See Known Issues page for details",
+          false);
+    }
+
     I2CJNI.i2CInitialize((byte) port.value);
 
     HAL.report(tResourceType.kResourceType_I2C, deviceAddress);