Change: replace per-AI "start_date" with a global "competitors_interval" (#10653)

The per-AI "start_date" is a lot of custom code, and was rarely
used in the way it was meant.

While at it, also ported this part over to the new timer system.

src/timer/timer_game_tick.cpp

@@ -0,0 +1,64 @@
+/*
+ * This file is part of OpenTTD.
+ * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
+ * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/**
+ * @file timer_game_tick.cpp
+ * This file implements the timer logic for the tick-based game-timer.
+ */
+
+#include "stdafx.h"
+#include "timer.h"
+#include "timer_game_tick.h"
+
+#include "safeguards.h"
+
+template<>
+void IntervalTimer<TimerGameTick>::Elapsed(TimerGameTick::TElapsed delta)
+{
+	if (this->period == 0) return;
+
+	this->storage.elapsed += delta;
+
+	uint count = 0;
+	while (this->storage.elapsed >= this->period) {
+		this->storage.elapsed -= this->period;
+		count++;
+	}
+
+	if (count > 0) {
+		this->callback(count);
+	}
+}
+
+template<>
+void TimeoutTimer<TimerGameTick>::Elapsed(TimerGameTick::TElapsed delta)
+{
+	if (this->fired) return;
+	if (this->period == 0) return;
+
+	this->storage.elapsed += delta;
+
+	if (this->storage.elapsed >= this->period) {
+		this->callback();
+		this->fired = true;
+	}
+}
+
+template<>
+void TimerManager<TimerGameTick>::Elapsed(TimerGameTick::TElapsed delta)
+{
+	for (auto timer : TimerManager<TimerGameTick>::GetTimers()) {
+		timer->Elapsed(delta);
+	}
+}
+
+#ifdef WITH_ASSERT
+template<>
+void TimerManager<TimerGameTick>::Validate(TimerGameTick::TPeriod period)
+{
+}
+#endif /* WITH_ASSERT */