[wpilibc] Transition C++ classes to units::second_t (#3396)

A lot of these are breaking changes. frc::Timer was replaced with the
contents of frc2::Timer. The others were in-place argument changes or
removing deprecated non-unit overloads.

wpilibNewCommands/src/main/native/cpp/frc2/command/CommandScheduler.cpp

@@ -359,12 +359,13 @@ void CommandScheduler::CancelAll() {
   Cancel(commands);
 }
 
-double CommandScheduler::TimeSinceScheduled(const Command* command) const {
+units::second_t CommandScheduler::TimeSinceScheduled(
+    const Command* command) const {
   auto find = m_impl->scheduledCommands.find(command);
   if (find != m_impl->scheduledCommands.end()) {
     return find->second.TimeSinceInitialized();
   } else {
-    return -1;
+    return -1_s;
   }
 }
 bool CommandScheduler::IsScheduled(