[wpilib] Update GetMatchTime docs and units (#5232)

wpilibc/src/main/native/cpp/DriverStation.cpp

@@ -582,9 +582,9 @@ bool DriverStation::WaitForDsConnection(units::second_t timeout) {
   return result;
 }
 
-double DriverStation::GetMatchTime() {
+units::second_t DriverStation::GetMatchTime() {
   int32_t status = 0;
-  return HAL_GetMatchTime(&status);
+  return units::second_t{HAL_GetMatchTime(&status)};
 }
 
 double DriverStation::GetBatteryVoltage() {

wpilibc/src/main/native/cpp/Timer.cpp

@@ -90,5 +90,5 @@ units::second_t Timer::GetFPGATimestamp() {
 }
 
 units::second_t Timer::GetMatchTime() {
-  return units::second_t{frc::DriverStation::GetMatchTime()};
+  return frc::DriverStation::GetMatchTime();
 }

wpilibc/src/main/native/include/frc/DriverStation.h

@@ -306,21 +306,26 @@ class DriverStation final {
   static bool WaitForDsConnection(units::second_t timeout);
 
   /**
-   * Return the approximate match time.
-   *
-   * The FMS does not send an official match time to the robots, but does send
-   * an approximate match time. The value will count down the time remaining in
-   * the current period (auto or teleop).
-   *
+   * Return the approximate match time. The FMS does not send an official match
+   * time to the robots, but does send an approximate match time. The value will
+   * count down the time remaining in the current period (auto or teleop).
    * Warning: This is not an official time (so it cannot be used to dispute ref
    * calls or guarantee that a function will trigger before the match ends).
    *
-   * The Practice Match function of the DS approximates the behavior seen on
-   * the field.
+   * <p>When connected to the real field, this number only changes in full
+   * integer increments, and always counts down.
    *
-   * @return Time remaining in current match period (auto or teleop)
+   * <p>When the DS is in practice mode, this number is a floating point number,
+   * and counts down.
+   *
+   * <p>When the DS is in teleop or autonomous mode, this number is a floating
+   * point number, and counts up.
+   *
+   * <p>Simulation matches DS behavior without an FMS connected.
+   *
+   * @return Time remaining in current match period (auto or teleop) in seconds
    */
-  static double GetMatchTime();
+  static units::second_t GetMatchTime();
 
   /**
    * Read the battery voltage.