Improve the editor audio preview inspector appearance and functionality

- Make the timeline indicator thicker and with an indicator triangle,
  similar to the animation editor timeline.
- Add Space bar shortcut to play/pause the audio preview.
- Only seek when clicking or dragging with the left mouse button,
  not other mouse buttons.

(cherry picked from commit a50a81b703910182b2b78bc4d2b16db5a97f20c6)

editor/plugins/audio_stream_editor_plugin.cpp

@@ -31,6 +31,7 @@
 #include "audio_stream_editor_plugin.h"
 
 #include "core/io/resource_loader.h"
+#include "core/os/keyboard.h"
 #include "core/project_settings.h"
 #include "editor/audio_stream_preview.h"
 #include "editor/editor_scale.h"
@@ -144,23 +145,26 @@ void AudioStreamEditor::_draw_indicator() {
 	Rect2 rect = _preview->get_rect();
 	float len = stream->get_length();
 	float ofs_x = _current / len * rect.size.width;
-	_indicator->draw_line(Point2(ofs_x, 0), Point2(ofs_x, rect.size.height), get_color("accent_color", "Editor"), 1);
+	const Color color = get_color("accent_color", "Editor");
+	_indicator->draw_line(Point2(ofs_x, 0), Point2(ofs_x, rect.size.height), color, Math::round(2 * EDSCALE));
+	_indicator->draw_texture(
+			get_icon("TimelineIndicator", "EditorIcons"),
+			Point2(ofs_x - get_icon("TimelineIndicator", "EditorIcons")->get_width() * 0.5, 0),
+			color);
 
 	_current_label->set_text(String::num(_current, 2).pad_decimals(2) + " /");
 }
 
 void AudioStreamEditor::_on_input_indicator(Ref<InputEvent> p_event) {
-	Ref<InputEventMouseButton> mb = p_event;
-
-	if (mb.is_valid()) {
+	const Ref<InputEventMouseButton> mb = p_event;
+	if (mb.is_valid() && mb->get_button_index() == BUTTON_LEFT) {
 		if (mb->is_pressed()) {
 			_seek_to(mb->get_position().x);
 		}
 		_dragging = mb->is_pressed();
 	}
 
-	Ref<InputEventMouseMotion> mm = p_event;
-
+	const Ref<InputEventMouseMotion> mm = p_event;
 	if (mm.is_valid()) {
 		if (_dragging) {
 			_seek_to(mm->get_position().x);
@@ -234,6 +238,7 @@ AudioStreamEditor::AudioStreamEditor() {
 	hbox->add_child(_play_button);
 	_play_button->set_focus_mode(Control::FOCUS_NONE);
 	_play_button->connect("pressed", this, "_play");
+	_play_button->set_shortcut(ED_SHORTCUT("inspector/audio_preview_play_pause", TTR("Audio Preview Play/Pause"), KEY_SPACE));
 
 	_stop_button = memnew(ToolButton);
 	hbox->add_child(_stop_button);