[wpilib] Add LED pattern API for easily animating addressable LEDs (#6344)

Add LEDReader and LEDWriter helper interfaces to facilitate composing simple patterns into more complex ones, e.g. LEDPattern.solid(Color.kBlue).breathe(Seconds.of(0.75)). Pattern composition relies on changing out the write behavior; for example, offsetBy increments the indexes to write to; while blink will switch between playing a base pattern and turning off all the LEDs.

Add a view class for splitting a single large buffer into smaller distinct sections, which is useful for dealing with long chained LED strips mounted on different parts of a robot. Views cannot be written directly to an LED strip (in fact, trying to do so won't even compile).

Adds some utility methods to the Color class for interpolating between two colors, and support color representations with 32-bit integers to avoid object allocations.

Co-authored-by: Tyler Veness <calcmogul@gmail.com>

wpilibcExamples/src/main/cpp/examples/AddressableLED/include/Robot.h

@@ -7,11 +7,11 @@
 #include <array>
 
 #include <frc/AddressableLED.h>
+#include <frc/LEDPattern.h>
 #include <frc/TimedRobot.h>
 
 class Robot : public frc::TimedRobot {
  public:
-  void Rainbow();
   void RobotInit() override;
   void RobotPeriodic() override;
 
@@ -23,6 +23,16 @@ class Robot : public frc::TimedRobot {
   frc::AddressableLED m_led{9};
   std::array<frc::AddressableLED::LEDData, kLength>
       m_ledBuffer;  // Reuse the buffer
-  // Store what the last hue of the first pixel is
-  int firstPixelHue = 0;
+
+  // Our LED strip has a density of 120 LEDs per meter
+  units::meter_t kLedSpacing{1 / 120.0};
+
+  // Create an LED pattern that will display a rainbow across
+  // all hues at maximum saturation and half brightness
+  frc::LEDPattern m_rainbow = frc::LEDPattern::Rainbow(255, 128);
+
+  // Create a new pattern that scrolls the rainbow pattern across the LED
+  // strip, moving at a speed of 1 meter per second.
+  frc::LEDPattern m_scrollingRainbow =
+      m_rainbow.ScrollAtAbsoluteSpeed(1_mps, kLedSpacing);
 };