Scene: Ensure classes match their header filename

Also drop some unused files.

Renamed:
- `scene/2d/navigation2d.h` -> `navigation_2d.h`
- `scene/2d/screen_button.h` -> `touch_screen_button.h`
- `scene/3d/scenario_fx.h` -> `world_environment.h`
- `scene/audio/audio_player.h` -> `audio_stream_player.h`
- `scene/resources/bit_mask.h` -> `bit_map.h`
- `scene/resources/color_ramp.h` -> `gradient.h`
- `scene/resources/shape_line_2d.h` -> `line_shape_2d.h`
- `scene/resources/scene_format_text.h` -> `resource_format_text.h`
- `scene/resources/sky_box.h` -> `sky.h`

Dropped:
- `scene/resources/bounds.h`

scene/audio/audio_stream_player.cpp

@@ -1,5 +1,5 @@
 /*************************************************************************/
-/*  audio_player.cpp                                                     */
+/*  audio_stream_player.cpp                                              */
 /*************************************************************************/
 /*                       This file is part of:                           */
 /*                           GODOT ENGINE                                */
@@ -28,7 +28,7 @@
 /* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
 /*************************************************************************/
 
-#include "audio_player.h"
+#include "audio_stream_player.h"
 
 #include "core/engine.h"
 

scene/audio/audio_stream_player.h

@@ -1,5 +1,5 @@
 /*************************************************************************/
-/*  audio_player.h                                                       */
+/*  audio_stream_player.h                                                */
 /*************************************************************************/
 /*                       This file is part of:                           */
 /*                           GODOT ENGINE                                */
@@ -28,8 +28,8 @@
 /* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
 /*************************************************************************/
 
-#ifndef AUDIOPLAYER_H
-#define AUDIOPLAYER_H
+#ifndef AUDIO_STREAM_PLAYER_H
+#define AUDIO_STREAM_PLAYER_H
 
 #include "scene/main/node.h"
 #include "servers/audio/audio_stream.h"
@@ -110,4 +110,5 @@ public:
 };
 
 VARIANT_ENUM_CAST(AudioStreamPlayer::MixTarget)
-#endif // AUDIOPLAYER_H
+
+#endif // AUDIO_STREAM_PLAYER_H