Add onDecorated property to decorated components

[chabou]

Plugins could be more powerful if we give them a way to retrieve a reference to decorated components.

The only reference that a plugin could have is htermby passing a onTerminal property.
It could use refproperty in decorators but if it is not the first in plugin list, it will receive previous plugin HOC.

With this PR, every plugin's decorate<Component> functions (decorateTerm, decorateTerms, decorateHeader, decorateTab...) could retrieve a reference to instance.

Maybe it is a little dangerous/anti-pattern to expose all instances to plugins, but this is the same logic than onTerminalproperty.

If you are ok with this feature, I'll add website documentation.

[chabou]

@rauchg @matheuss @ppot could you give me your opinion about this feature ?

[rauchg]

Wouldn't there be a way for getting the instance yourself when you decorate though?

[chabou]

If you are the only (or the first) plugin, there is a way by passing : refproperty when rendering Term because it is a first level child. But if you are the second plugin, you are not decorating Term itself but the first plugin decorator. If this first plugin doesn't keep a reference to Term instance (using refproperty), I think there is no way to find it (but maybe I'm wrong).

[chabou]

This reason leads to add onTerminal() capability to plugin decorator.
This PR generalize this capability (and could replace it) to all component that could be decorated.

[chabou]

@rauchg I really think that this PR is a good idea 😊

[rauchg]

I completely agree. Thanks for your explanation. We need to document this on the website, however.