tooltip: Don't save style overrides to tooltip.tscn

Previously, if you opened tooltip.tscn in the editor and hit Save, its
`_ready()` method would persist the style overrides we use to apply the editor
theme's fonts to the label. This isn't necessary, or desirable.

Don't apply the style overrides if the tooltip scene itself is being edited.

https://phabricator.endlessm.com/T35540

Author: wjt

addons/block_code/ui/tooltip/tooltip.gd

@@ -3,14 +3,16 @@ class_name Tooltip
 extends RichTextLabel
 ## Rich-text control for block tooltips that matches the built-in inspector's tooltips' font styles
 
+const Util = preload("res://addons/block_code/ui/util.gd")
+
 
 func override_font(font_name: StringName, editor_font_name: StringName) -> Font:
 	var font = get_theme_font(editor_font_name, &"EditorFonts")
 	add_theme_font_override(font_name, font)
 	return font
 
 
-func _ready():
+func override_fonts():
 	# Set fonts to match documentation tooltips in inspector
 	override_font(&"normal_font", &"doc")
 	override_font(&"mono_font", &"doc_source")
@@ -22,3 +24,8 @@ func _ready():
 	bold_italics.set_base_font(italics)
 	bold_italics.set_variation_embolden(1.2)
 	add_theme_font_override(&"bold_italics_font", bold_italics)
+
+
+func _ready():
+	if not Util.node_is_part_of_edited_scene(self):
+		override_fonts()