[wpimath] Add lastValue() method to filters (#6351)

wpimath/src/main/java/edu/wpi/first/math/filter/LinearFilter.java

@@ -313,6 +313,15 @@ public class LinearFilter {
     return retVal;
   }
 
+  /**
+   * Returns the last value calculated by the LinearFilter.
+   *
+   * @return The last value.
+   */
+  public double lastValue() {
+    return m_outputs.getFirst();
+  }
+
   /**
    * Factorial of n.
    *

wpimath/src/main/java/edu/wpi/first/math/filter/MedianFilter.java

@@ -72,6 +72,15 @@ public class MedianFilter {
     }
   }
 
+  /**
+   * Returns the last value calculated by the MedianFilter.
+   *
+   * @return The last value.
+   */
+  public double lastValue() {
+    return m_valueBuffer.getFirst();
+  }
+
   /** Resets the filter, clearing the window of all elements. */
   public void reset() {
     m_orderedValues.clear();

wpimath/src/main/java/edu/wpi/first/math/filter/SlewRateLimiter.java

@@ -64,6 +64,15 @@ public class SlewRateLimiter {
     return m_prevVal;
   }
 
+  /**
+   * Returns the value last calculated by the SlewRateLimiter.
+   *
+   * @return The last value.
+   */
+  public double lastValue() {
+    return m_prevVal;
+  }
+
   /**
    * Resets the slew rate limiter to the specified value; ignores the rate limit when doing so.
    *