Drivers, main, servers: Ensure classes match their header filename

Renamed:
- `drivers/alsamidi/alsa_midi.h` -> `midi_driver_alsamidi.h`
  (same for `coremidi` and `winmidi`)
- `main/timer_sync.h` -> `main_timer_sync.h`
- `servers/visual/visual_server_global.h` -> `visual_server_globals.h`

drivers/alsamidi/midi_driver_alsamidi.cpp

@@ -1,5 +1,5 @@
 /*************************************************************************/
-/*  alsa_midi.cpp                                                        */
+/*  midi_driver_alsamidi.cpp                                             */
 /*************************************************************************/
 /*                       This file is part of:                           */
 /*                           GODOT ENGINE                                */
@@ -30,7 +30,7 @@
 
 #ifdef ALSAMIDI_ENABLED
 
-#include "alsa_midi.h"
+#include "midi_driver_alsamidi.h"
 
 #include "core/os/os.h"
 #include "core/print_string.h"
@@ -199,4 +199,4 @@ MIDIDriverALSAMidi::~MIDIDriverALSAMidi() {
 	close();
 }
 
-#endif
+#endif // ALSAMIDI_ENABLED

drivers/alsamidi/midi_driver_alsamidi.h

@@ -1,5 +1,5 @@
 /*************************************************************************/
-/*  alsa_midi.h                                                          */
+/*  midi_driver_alsamidi.h                                               */
 /*************************************************************************/
 /*                       This file is part of:                           */
 /*                           GODOT ENGINE                                */
@@ -30,8 +30,8 @@
 
 #ifdef ALSAMIDI_ENABLED
 
-#ifndef ALSA_MIDI_H
-#define ALSA_MIDI_H
+#ifndef MIDI_DRIVER_ALSAMIDI_H
+#define MIDI_DRIVER_ALSAMIDI_H
 
 #include "core/os/midi_driver.h"
 #include "core/os/mutex.h"
@@ -65,5 +65,5 @@ public:
 	virtual ~MIDIDriverALSAMidi();
 };
 
-#endif
-#endif
+#endif // MIDI_DRIVER_ALSAMIDI_H
+#endif // ALSAMIDI_ENABLED