Restyle the music player bar

The bar is rounded and a little taller, with a round orange play button
and a restart button that lights up orange under the mouse. The icons sit
inside their buttons with room around them, and are one colour, cropped to
their shape. Progress fills in orange, the volume slider gets a speaker
icon, and the buttons say their shortcut keys in their tooltips.

Buttons grow a little under the mouse and shrink while held down, and the
play button pops when it switches between play and pause. ButtonBounce
holds these animations so other buttons can use them too.

player/music_player.gd

@@ -2,19 +2,22 @@ class_name MusicPlayer
 extends Control
 ## The bar that plays the songs, with play, restart, progress and volume. Whether a song
 ## repeats is a quiz setting ([code]Settings.auto_repeat_song[/code]).
+##
+## The buttons grow a little under the mouse and the play button pops when it switches
+## between play and pause, see [ButtonBounce].
 
 signal update_song_list
 signal play_next_song
 
-var play_icon: Texture = preload("res://icons/play_icon_light.svg")
-var pause_icon: Texture = preload("res://icons/pause_icon_light.svg")
+var play_icon: Texture = preload("res://icons/play_button_icon.svg")
+var pause_icon: Texture = preload("res://icons/pause_button_icon.svg")
 var is_changing: bool = false
 var playback_position: float
 var stream: AudioStream
 var song_finished: bool = false
 
-@onready var play_button: TextureButton = %PlayTextureButton
-@onready var restart_button: TextureButton = %RestartTextureButton
+@onready var play_button: Button = %PlayButton
+@onready var restart_button: Button = %RestartButton
 @onready var audio_player: AudioStreamPlayer = $AudioStreamPlayer
 @onready var sound_player: AudioStreamPlayer = $AudioSoundPlayer
 @onready var sound_effect_player: AudioStreamPlayer = $AudioSoundEffectPlayer
@@ -26,6 +29,8 @@ var song_finished: bool = false
 func _ready() -> void:
 	play_button.pressed.connect(play_or_pause)
 	restart_button.pressed.connect(restart)
+	ButtonBounce.add_to(play_button)
+	ButtonBounce.add_to(restart_button)
 	progress_slider.drag_started.connect(_on_drag_started)
 	progress_slider.drag_ended.connect(_on_drag_ended)
 
@@ -43,6 +48,19 @@ func _process(_delta: float) -> void:
 			music_time_label.text = format_text(progress_slider.value, 0.0)
 
 
+## Whether the play button shows pause, because a song is playing.
+func shows_playing() -> bool:
+	return play_button.icon == pause_icon
+
+
+# Shows pause on the play button while a song plays, and play otherwise
+func _show_playing(playing: bool) -> void:
+	var icon: Texture = pause_icon if playing else play_icon
+	if play_button.icon != icon:
+		play_button.icon = icon
+		ButtonBounce.pop(play_button)
+
+
 func format_time(time: float) -> String:
 	var total_seconds: int = roundi(time)
 	@warning_ignore("integer_division")
@@ -64,7 +82,7 @@ func play_or_pause() -> void:
 	if song_finished:
 		restart()
 	elif audio_player.stream_paused:
-		play_button.texture_normal = pause_icon
+		_show_playing(true)
 		audio_player.stream_paused = false
 		song_finished = false
 		audio_player.seek(playback_position)
@@ -81,7 +99,7 @@ func play_or_pause() -> void:
 func pause() -> void:
 	audio_player.stream_paused = true
 	playback_position = audio_player.get_playback_position()
-	play_button.texture_normal = play_icon
+	_show_playing(false)
 
 
 func restart() -> void:
@@ -91,12 +109,12 @@ func restart() -> void:
 	progress_slider.value = 0
 	playback_position = audio_player.get_playback_position()
 	audio_player.seek(playback_position)
-	play_button.texture_normal = pause_icon
+	_show_playing(true)
 	audio_player.play()
 
 
 func _on_finished() -> void:
-	play_button.texture_normal = play_icon
+	_show_playing(false)
 	song_finished = true
 	if !Settings.stop_after_current:
 		play_next_song.emit()
@@ -150,7 +168,7 @@ func play_sound(sound_name: AudioStream) -> void:
 	audio_player.stop()
 	sound_player.play()
 	song_finished = true
-	play_button.texture_normal = play_icon
+	_show_playing(false)
 	progress_slider.value = 0
 
 
@@ -159,7 +177,7 @@ func play_song(song: AudioStream) -> void:
 	audio_player.play()
 	sound_player.stop()
 	song_finished = false
-	play_button.texture_normal = pause_icon
+	_show_playing(true)
 	stream = audio_player.stream
 	progress_slider.value = 0
 	progress_slider.max_value = round(stream.get_length())
@@ -179,7 +197,7 @@ func play_song_object(song_object_no: int) -> void:
 	sound_player.stop()
 	audio_player.play()
 	song_finished = false
-	play_button.texture_normal = pause_icon
+	_show_playing(true)
 	stream = audio_player.stream
 	progress_slider.value = 0
 	progress_slider.max_value = round(stream.get_length())