Clarify icon location

The Metatype Service specification states for the location value of the icon element (Table 105.1 in section 105.7.1):

The resource is a URL. The base URL is assumed to be the XML file
with the definition. I.e. if the XML is a resource in the JAR file, then this
URL can reference another resource in that JAR file using a relative URL.

Our current implementation takes this definition and uses the XML resource URL as the base URL to create the Icon URL.

For example: If the icon resource path is "icon/sample.png" and the XML resource URL is "file://bundle-5/OSGI-INF/metatype/sample.xml" then the icon resource URL would be assumed to be "file://bundle-5/OSGI-INF/icon/sample.png".

In contrast the current OSGi CT work-in-progress expects the URL to be relative to the defining bundle.

It must be clarified which reading is correct.