[MCHANGES-412] Allow an action to carry an optional scope

**[Gary D. Gregory](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=garydgregory)** opened **[MCHANGES-412](https://issues.apache.org/jira/browse/MCHANGES-412?redirect=false)** and commented

In changes.xml, I would like an **action** to carry an optional {**}scope{**}.

This would help users understand what changes affect which part of their projects.

For example:

Fix some bug\
Bump dependency foo from 1 to 2\
Bump commons-parent foo from 1 to 2\
Documented this and that\

The use of the scope documents where the change applies, usually runtime, test, or build, but it could be string maybe.

This somewhat parallels the concept of a scope in a dependency so the value set could be the same as allowed for a dependency scope but that might be too restrictive.

Thoughts?

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No further details from [MCHANGES-412](https://issues.apache.org/jira/browse/MCHANGES-412?redirect=false)

changes.xml の action の例から始め、action 属性が plugin 内でどのように表現され、使用されているかを追跡します。オプションの scope の動作と受け入れられる値を定義し、scope を持つ action が受け入れられ、その scope がユーザーに表示されることを、scope を省略した action を壊さずに検証します。

索引モデルが issue の本文から書いたものです。