Document legacy action modifier interaction with component event handlers

[olenderhub]

This adds a legacy note to the @ember/component API docs under the "Event Handler Methods" section.

Issue #17877 asked about documenting ordering semantics between classic component event handler methods, legacy {{action}}, and actions forwarded through ...attributes. Since {{action}} is no longer available in current Ember, this note avoids documenting it as current API and instead points readers to {{on}}.

The note links to the template-action deprecation guide for migration details.

I intentionally avoided stating a specific same-element ordering because I could not find an existing test covering classic component event handlers and {{action}} on the same element. The note only calls out that this combination relied on legacy event dispatching and had subtle ordering semantics.

Refs #17877

[NullVoxPopuli]

since {{action}} is no longer available, is this comment still relevant? is there code we can cleanup around this behavior instead?

[olenderhub]

@NullVoxPopuli I see what you mean. I picked this up because #17877 and #17877 (comment) seemed to ask for documentation around this legacy interaction.

Given that {{action}} is no longer available in current Ember, does it make sense to close #17877? If so, I can close this PR too.