Decrease font placeholder opacity in the editor theme

This makes placeholder text easier to distinguish from actual text
in the editor. Previously, placeholder text's contrast against the
background was only slightly lower than actual text.

editor/themes/editor_theme_manager.cpp

@@ -472,7 +472,7 @@ void EditorThemeManager::_create_shared_styles(const Ref<EditorTheme> &p_theme,
 		p_config.font_hover_pressed_color = p_config.font_hover_color.lerp(p_config.accent_color, 0.74);
 		p_config.font_disabled_color = Color(p_config.mono_color.r, p_config.mono_color.g, p_config.mono_color.b, 0.35);
 		p_config.font_readonly_color = Color(p_config.mono_color.r, p_config.mono_color.g, p_config.mono_color.b, 0.65);
-		p_config.font_placeholder_color = Color(p_config.mono_color.r, p_config.mono_color.g, p_config.mono_color.b, 0.6);
+		p_config.font_placeholder_color = Color(p_config.mono_color.r, p_config.mono_color.g, p_config.mono_color.b, 0.5);
 		p_config.font_outline_color = Color(0, 0, 0, 0);
 
 		p_theme->set_color(SceneStringName(font_color), EditorStringName(Editor), p_config.font_color);