UI::Toolbar#get_last_state refer to magic numbers instead of constants

[thomthom]

https://ruby.sketchup.com/UI/Toolbar.html#get_last_state-instance_method

Better to refer to the constants:

https://ruby.sketchup.com/top-level-namespace.html#constants_for_toolbar_states

[kalpana-ghodeswar]

Logged SKEXT-4703