Feat: Add id attribute (gav) support to Dependency, Exclusion, Mixin

[rbygrave]

Based on design discussion on Issue #11500, the proposal is to support groupId:artifactId:version format for Dependency, Exclusion and Mixin elements.

This means that we can define dependencies in the form:

<dependency id="groupId:artifactId:version" />

Examples:

<dependency id="org.slf4j:slf4j-api:2.0.17"/>

<dependency id="org.postgresql:postgresql:42.7.3">
  <exclusions>
    <exclusion id="*:*"/>
  </exclusions>
</dependency>

<mixin id="com.example.mixins:java-mixin:1.0.0" />

Notes:

• Mixin has the xml attribute id but uses gav underneath as the java field. This was because Mixin extends Parent which already has getId(). This was done to effectively work around the name clash with id there.

• The validation is strict meaning that it's deemed invalid to mix the use of id attribute with the usual gav elements. That is, when we use id it's deemed invalid to set a groupId or artifactId or version. Maybe this strict validation could be lossened up but to me it seems reasonable to start with this strict validation initially.

• In Support groupId: artifactId: version format #11500 it was mentioned about also having attributes for scope and classification etc but that is omitted from this change. To specify scope we must still use the scope element.

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[rbygrave]

Using field name gav with attribute name id ... in order to avoid the conflict with the existing Parent.getId()