[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/commands/turndegrees.py

@@ -0,0 +1,57 @@
+#
+# 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
+
+from subsystems.drivetrain import Drivetrain
+
+
+class TurnDegrees(commands2.Command):
+    def __init__(self, velocity: float, degrees: float, drive: Drivetrain) -> None:
+        """Creates a new TurnDegrees. This command will turn your robot for a desired rotation (in
+        degrees) and rotational velocity.
+
+        :param velocity:   The velocity which the robot will drive. Negative is in reverse.
+        :param degrees: Degrees to turn. Leverages encoders to compare distance.
+        :param drive:   The drive subsystem on which this command will run
+        """
+
+        self.degrees = degrees
+        self.velocity = velocity
+        self.drive = drive
+        self.addRequirements(drive)
+
+    def initialize(self) -> None:
+        """Called when the command is initially scheduled."""
+        # Set motors to stop, read encoder values for starting point
+        self.drive.arcadeDrive(0, 0)
+        self.drive.resetEncoders()
+
+    def execute(self) -> None:
+        """Called every time the scheduler runs while the command is scheduled."""
+        self.drive.arcadeDrive(0, self.velocity)
+
+    def end(self, interrupted: bool) -> None:
+        """Called once the command ends or is interrupted."""
+        self.drive.arcadeDrive(0, 0)
+
+    def isFinished(self) -> bool:
+        """Returns true when the command should end."""
+
+        # Need to convert distance travelled to degrees. The Standard
+        # XRP Chassis found here, https://www.sparkfun.com/products/22230,
+        # has a wheel placement diameter (163 mm) - width of the wheel (8 mm) = 155 mm
+        # or 6.102 inches. We then take into consideration the width of the tires.
+        inchPerDegree = math.pi * 6.102 / 360
+
+        # Compare distance travelled from start to distance based on degree turn
+        return self._getAverageTurningDistance() >= inchPerDegree * self.degrees
+
+    def _getAverageTurningDistance(self) -> float:
+        leftDistance = abs(self.drive.getLeftDistanceInch())
+        rightDistance = abs(self.drive.getRightDistanceInch())
+        return (leftDistance + rightDistance) / 2.0