Increase the default AudioStreamPlayer3D unit size to 10

This makes it easier to hear sound while setting up the node.

Since this changes the default value, this may break existing projects
slightly.

This also tweaks the Unit Size editor property hint for better usability.

See discussion in #25468.

doc/classes/AudioStreamPlayer3D.xml

@@ -108,7 +108,7 @@
 		<member name="unit_db" type="float" setter="set_unit_db" getter="get_unit_db" default="0.0">
 			The base sound level unaffected by dampening, in decibels.
 		</member>
-		<member name="unit_size" type="float" setter="set_unit_size" getter="get_unit_size" default="1.0">
+		<member name="unit_size" type="float" setter="set_unit_size" getter="get_unit_size" default="10.0">
 			The factor for the attenuation effect. Higher values make the sound audible over a larger distance.
 		</member>
 	</members>

scene/3d/audio_stream_player_3d.cpp

@@ -964,7 +964,7 @@ void AudioStreamPlayer3D::_bind_methods() {
 	ADD_PROPERTY(PropertyInfo(Variant::OBJECT, "stream", PROPERTY_HINT_RESOURCE_TYPE, "AudioStream"), "set_stream", "get_stream");
 	ADD_PROPERTY(PropertyInfo(Variant::INT, "attenuation_model", PROPERTY_HINT_ENUM, "Inverse,InverseSquare,Log,Disabled"), "set_attenuation_model", "get_attenuation_model");
 	ADD_PROPERTY(PropertyInfo(Variant::FLOAT, "unit_db", PROPERTY_HINT_RANGE, "-80,80"), "set_unit_db", "get_unit_db");
-	ADD_PROPERTY(PropertyInfo(Variant::FLOAT, "unit_size", PROPERTY_HINT_RANGE, "0.1,100,0.1"), "set_unit_size", "get_unit_size");
+	ADD_PROPERTY(PropertyInfo(Variant::FLOAT, "unit_size", PROPERTY_HINT_RANGE, "0.1,100,0.01,or_greater"), "set_unit_size", "get_unit_size");
 	ADD_PROPERTY(PropertyInfo(Variant::FLOAT, "max_db", PROPERTY_HINT_RANGE, "-24,6"), "set_max_db", "get_max_db");
 	ADD_PROPERTY(PropertyInfo(Variant::FLOAT, "pitch_scale", PROPERTY_HINT_RANGE, "0.01,4,0.01,or_greater"), "set_pitch_scale", "get_pitch_scale");
 	ADD_PROPERTY(PropertyInfo(Variant::BOOL, "playing", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_EDITOR), "_set_playing", "is_playing");

scene/3d/audio_stream_player_3d.h

@@ -98,7 +98,7 @@ private:
 
 	AttenuationModel attenuation_model = ATTENUATION_INVERSE_DISTANCE;
 	float unit_db = 0.0;
-	float unit_size = 1.0;
+	float unit_size = 10.0;
 	float max_db = 3.0;
 	float pitch_scale = 1.0;
 	bool autoplay = false;