ColorPicker: Add intensity slider

Add intensity slider to all color modes. Replace raw mode by linear mode, which uses linear color space.

When color is overbright, automatically switch hex text to script text. Allow executing expression in script text field to set color. Add the "script" icon to the default theme.

scene/theme/default_theme.cpp

@@ -1055,6 +1055,7 @@ void fill_default_theme(Ref<Theme> &theme, const Ref<Font> &default_font, const
 	theme->set_icon("bar_arrow", "ColorPicker", icons["color_picker_bar_arrow"]);
 	theme->set_icon("picker_cursor", "ColorPicker", icons["color_picker_cursor"]);
 	theme->set_icon("picker_cursor_bg", "ColorPicker", icons["color_picker_cursor_bg"]);
+	theme->set_icon("color_script", "ColorPicker", icons["script"]);
 
 	{
 		const int precision = 7;

scene/theme/icons/script.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16"><path fill="#e0e0e0" d="M6 1a2 2 0 0 0-2 2v7H1v3a2 2 0 0 0 2 2h7a2 2 0 0 0 2-2V5h3V3a2 2 0 0 0-2-2z"/><path fill-opacity=".2" d="M6 1a2 2 0 0 0-2 2v7H1v3a2 2 0 1 0 4 0V3a1 1 0 0 1 2 0v3h5V5H8V3a2 2 0 0 0-2-2zM2 11h2v2a1 1 0 0 1-2 0z"/></svg>