Test and document the standard component lifecycle events

[bob2517]

It's a easy forgotten fact, by me mainly, that Active CSS shadow DOM components do actually support the standard shadow DOM component lifecycle events, as well as beforeComponentOpen and componentOpen.

I just don't use them. I don't need to clean-up anything with disconnectedCallback as everything related to a component is removed when a component is removed. But it's probably just a matter of time and use cases, as everything usually is.

So test these and specify how to use them in the documentation...

[bob2517]

This does need doing - tagging for 2.15.0 milestone.

[bob2517]

The following events are now supported on the branch:

&:connectedCallback (pseudonym for &:beforeComponentOpen)
&:disconnectedCallback (when detecting the removal of an element)
&:attrChange[Name of attribute] (to detect changes to attribute via an event)

To get the attribute value inside the change event, if not using them reactively with the double-curly syntax, you use the {@host:attr} syntax. For example if monitoring the attribute "cheese" in a custom element component:

&:attrChangeCheese {
    console-log: "attribute changed from {@host:cheese-old}" to {@host:cheese}.";
}

The value of the attribute prior to the change is available by adding a "-old" to the name of the attribute.

[bob2517]

Closing pending release