[robotpy][examples] Split examples and snippets (#8944)

This also updates the bazel scripts to behave more like the C++ and Java
examples, and updates the copybara scripts to be able to sync up
`mostrobotpy`

robotpyExamples/examples/XrpReference/subsystems/drivetrain.py

@@ -0,0 +1,115 @@
+#
+# Copyright (c) FIRST and other WPILib contributors.
+# Open Source Software; you can modify and/or share it under the terms of
+# the WPILib BSD license file in the root directory of this project.
+#
+
+import math
+
+import commands2
+import wpilib
+import wpiutil
+import xrp
+
+
+class Drivetrain(commands2.Subsystem):
+    kGearRatio = (30.0 / 14.0) * (28.0 / 16.0) * (36.0 / 9.0) * (26.0 / 8.0)  #  48.75:1
+    kCountsPerMotorShaftRev = 12.0
+    kCountsPerRevolution = kCountsPerMotorShaftRev * kGearRatio  # 585.0
+    kWheelDiameterInch = 2.3622  # 60 mm
+
+    def __init__(self) -> None:
+
+        # The XRP has the left and right motors set to
+        # PWM channels 0 and 1 respectively
+        self.leftMotor = xrp.XRPMotor(0)
+        self.rightMotor = xrp.XRPMotor(1)
+
+        # The XRP has onboard encoders that are hardcoded
+        # to use DIO pins 4/5 and 6/7 for the left and right
+        self.leftEncoder = wpilib.Encoder(4, 5)
+        self.rightEncoder = wpilib.Encoder(6, 7)
+
+        # Set up the differential drive controller
+        self.drive = wpilib.DifferentialDrive(
+            self.leftMotor.setThrottle, self.rightMotor.setThrottle
+        )
+
+        # TODO: these don't work
+        # wpiutil.SendableRegistry.addChild(self.drive, self.leftMotor)
+        # wpiutil.SendableRegistry.addChild(self.drive, self.rightMotor)
+
+        # Set up the XRPGyro
+        self.gyro = xrp.XRPGyro()
+
+        # We need to invert one side of the drivetrain so that positive voltages
+        # result in both sides moving forward. Depending on how your robot's
+        # gearbox is constructed, you might have to invert the left side instead.
+        self.rightMotor.setInverted(True)
+
+        # Use inches as unit for encoder distances
+        self.leftEncoder.setDistancePerPulse(
+            (math.pi * self.kWheelDiameterInch) / self.kCountsPerRevolution
+        )
+        self.rightEncoder.setDistancePerPulse(
+            (math.pi * self.kWheelDiameterInch) / self.kCountsPerRevolution
+        )
+        self.resetEncoders()
+
+    def arcadeDrive(self, xaxisVelocity: float, zaxisRotate: float) -> None:
+        """
+        Drives the robot using arcade controls.
+
+        :param xaxisVelocity: the commanded forward movement
+        :param zaxisRotate: the commanded rotation
+        """
+        self.drive.arcadeDrive(xaxisVelocity, zaxisRotate)
+
+    def resetEncoders(self) -> None:
+        """Resets the drive encoders to currently read a position of 0."""
+        self.leftEncoder.reset()
+        self.rightEncoder.reset()
+
+    def getLeftEncoderCount(self) -> int:
+        return self.leftEncoder.get()
+
+    def getRightEncoderCount(self) -> int:
+        return self.rightEncoder.get()
+
+    def getLeftDistanceInch(self) -> float:
+        return self.leftEncoder.getDistance()
+
+    def getRightDistanceInch(self) -> float:
+        return self.rightEncoder.getDistance()
+
+    def getAverageDistanceInch(self) -> float:
+        """Gets the average distance of the TWO encoders."""
+        return (self.getLeftDistanceInch() + self.getRightDistanceInch()) / 2.0
+
+    def getGyroAngleX(self) -> float:
+        """Current angle of the Romi around the X-axis.
+
+        :returns: The current angle of the Romi in degrees
+        """
+        return self.gyro.getAngleX()
+
+    def getGyroAngleY(self) -> float:
+        """Current angle of the Romi around the Y-axis.
+
+        :returns: The current angle of the Romi in degrees
+        """
+        return self.gyro.getAngleY()
+
+    def getGyroAngleZ(self) -> float:
+        """Current angle of the Romi around the Z-axis.
+
+        :returns: The current angle of the Romi in degrees
+        """
+        return self.gyro.getAngleZ()
+
+    def resetGyro(self) -> None:
+        """Reset the gyro"""
+        self.gyro.reset()
+
+    def periodic(self) -> None:
+        """This method will be called once per scheduler run"""