[wpimath] Replace pi with symbol in docs (#7322)

wpimath/src/main/java/edu/wpi/first/math/MathUtil.java

@@ -126,7 +126,7 @@ public final class MathUtil {
   }
 
   /**
-   * Wraps an angle to the range -pi to pi radians.
+   * Wraps an angle to the range -π to π radians.
    *
    * @param angleRadians Angle to wrap in radians.
    * @return The wrapped angle.

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

@@ -80,7 +80,7 @@ public class LinearFilter {
    * Creates a one-pole IIR low-pass filter of the form: y[n] = (1-gain) x[n] + gain y[n-1] where
    * gain = e<sup>-dt / T</sup>, T is the time constant in seconds.
    *
-   * <p>Note: T = 1 / (2 pi f) where f is the cutoff frequency in Hz, the frequency above which the
+   * <p>Note: T = 1 / (2πf) where f is the cutoff frequency in Hz, the frequency above which the
    * input starts to attenuate.
    *
    * <p>This filter is stable for time constants greater than zero.
@@ -101,7 +101,7 @@ public class LinearFilter {
    * Creates a first-order high-pass filter of the form: y[n] = gain x[n] + (-gain) x[n-1] + gain
    * y[n-1] where gain = e<sup>-dt / T</sup>, T is the time constant in seconds.
    *
-   * <p>Note: T = 1 / (2 pi f) where f is the cutoff frequency in Hz, the frequency below which the
+   * <p>Note: T = 1 / (2πf) where f is the cutoff frequency in Hz, the frequency below which the
    * input starts to attenuate.
    *
    * <p>This filter is stable for time constants greater than zero.

wpimath/src/main/java/edu/wpi/first/math/geometry/Rotation2d.java

@@ -164,7 +164,7 @@ public class Rotation2d
   }
 
   /**
-   * Adds two rotations together, with the result being bounded between -pi and pi.
+   * Adds two rotations together, with the result being bounded between -π and π.
    *
    * <p>For example, <code>Rotation2d.fromDegrees(30).plus(Rotation2d.fromDegrees(60))</code> equals
    * <code>Rotation2d(Math.PI/2.0)</code>
@@ -251,7 +251,7 @@ public class Rotation2d
    * Returns the radian value of the Rotation2d.
    *
    * @return The radian value of the Rotation2d.
-   * @see edu.wpi.first.math.MathUtil#angleModulus(double) to constrain the angle within (-pi, pi]
+   * @see edu.wpi.first.math.MathUtil#angleModulus(double) to constrain the angle within (-π, π]
    */
   @JsonProperty
   public double getRadians() {