[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/Mechanism2d/robot.py

@@ -0,0 +1,60 @@
+#!/usr/bin/env python3
+#
+# 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 wpilib
+import wpiutil
+
+
+class MyRobot(wpilib.TimedRobot):
+    """
+    This sample program shows how to use Mechanism2d - a visual representation of arms, elevators,
+    and other mechanisms on dashboards; driven by a node-based API.
+
+    Ligaments are based on other ligaments or roots, and roots are contained in the base
+    Mechanism2d object.
+    """
+
+    kMetersPerPulse = 0.01
+    kElevatorMinimumLength = 0.5
+
+    def __init__(self):
+        super().__init__()
+        self.elevatorMotor = wpilib.PWMSparkMax(0)
+        self.wristMotor = wpilib.PWMSparkMax(1)
+        self.wristPot = wpilib.AnalogPotentiometer(1, 90)
+        self.elevatorEncoder = wpilib.Encoder(0, 1)
+        self.joystick = wpilib.Joystick(0)
+
+        self.elevatorEncoder.setDistancePerPulse(self.kMetersPerPulse)
+
+        # the main mechanism object
+        self.mech = wpilib.Mechanism2d(3, 3)
+        # the mechanism root node
+        self.root = self.mech.getRoot("climber", 2, 0)
+
+        # MechanismLigament2d objects represent each "section"/"stage" of the mechanism, and are based
+        # off the root node or another ligament object
+        self.elevator = self.root.appendLigament(
+            "elevator", self.kElevatorMinimumLength, 90
+        )
+        self.wrist = self.elevator.appendLigament(
+            "wrist", 0.5, 90, 6, wpiutil.Color8Bit(wpiutil.Color.PURPLE)
+        )
+
+        # post the mechanism to the dashboard
+        wpilib.SmartDashboard.putData("Mech2d", self.mech)
+
+    def robotPeriodic(self):
+        # update the dashboard mechanism's state
+        self.elevator.setLength(
+            self.kElevatorMinimumLength + self.elevatorEncoder.getDistance()
+        )
+        self.wrist.setAngle(self.wristPot.get())
+
+    def teleopPeriodic(self):
+        self.elevatorMotor.setThrottle(self.joystick.getRawAxis(0))
+        self.wristMotor.setThrottle(self.joystick.getRawAxis(1))