global_properties are silently immutable

[ekr-cfa]

If you try to set the same global property twice, it succeeds but only the first value is used:

    #[test]
    fn set_get_global_property_twice() {
        let params: ParamType = ParamType {
            days: 10,
            diseases: 2,
        };
        let mut context = Context::new();
        context.set_global_property_value(DiseaseParams, params.clone());
        let global_params = context.get_global_property_value(DiseaseParams).clone();
        assert_eq!(global_params.days, params.days);
        assert_eq!(global_params.diseases, params.diseases);
        let params2: ParamType = ParamType {
            days: 11,
            diseases: 3,
        };
        context.set_global_property_value(DiseaseParams, params2.clone());
        assert_eq!(global_params.days, params2.days);
        assert_eq!(global_params.diseases, params2.diseases);
        
    }

Output:

thread 'global_properties::test::set_get_global_property_twice' panicked at src/global_properties.rs:218:9:
assertion `left == right` failed
  left: 10
 right: 11

The source of the problem is:

    fn set_global_property_value<T: GlobalProperty + 'static>(
        &mut self,
        _property: &T,
        value: T::Value,
    ) {
        let _data_container = self
            .global_property_container
            .entry(TypeId::of::<T>())
            .or_insert_with(|| Box::new(value));
    }

This should either be .insert() which would make properties mutable, or .try_insert()? and then return a Result<T>.

But it's bad to have the API appear to succeed but not do anything.

[ekr-cfa]

@k88hudson-cfa @confunguido