[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/MecanumBot/robot.py

@@ -0,0 +1,58 @@
+#!/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 wpimath
+import wpilib
+
+from drivetrain import Drivetrain
+
+
+class MyRobot(wpilib.TimedRobot):
+    def __init__(self) -> None:
+        super().__init__()
+
+        self.controller = wpilib.NiDsXboxController(0)
+        self.mecanum = Drivetrain()
+
+        # Slew rate limiters to make joystick inputs more gentle; 1/3 sec from 0 to 1.
+        self.xvelocityLimiter = wpimath.SlewRateLimiter(3)
+        self.yvelocityLimiter = wpimath.SlewRateLimiter(3)
+        self.rotLimiter = wpimath.SlewRateLimiter(3)
+
+    def autonomousPeriodic(self) -> None:
+        self.driveWithJoystick(False)
+        self.mecanum.updateOdometry()
+
+    def teleopPeriodic(self) -> None:
+        self.driveWithJoystick(True)
+
+    def driveWithJoystick(self, fieldRelative: bool) -> None:
+        # Get the x velocity. We are inverting this because Xbox controllers return
+        # negative values when we push forward.
+        xVelocity = (
+            -self.xvelocityLimiter.calculate(self.controller.getLeftY())
+            * Drivetrain.MAX_VELOCITY
+        )
+
+        # Get the y velocity or sideways/strafe velocity. We are inverting this because
+        # we want a positive value when we pull to the left. Xbox controllers
+        # return positive values when you pull to the right by default.
+        yVelocity = (
+            -self.yvelocityLimiter.calculate(self.controller.getLeftX())
+            * Drivetrain.MAX_VELOCITY
+        )
+
+        # Get the rate of angular rotation. We are inverting this because we want a
+        # positive value when we pull to the left (remember, CCW is positive in
+        # mathematics). Xbox controllers return positive values when you pull to
+        # the right by default.
+        rot = (
+            -self.rotLimiter.calculate(self.controller.getRightX())
+            * Drivetrain.MAX_ANGULAR_VELOCITY
+        )
+
+        self.mecanum.drive(xVelocity, yVelocity, rot, fieldRelative, self.getPeriod())