[MSHARED-1364] AbstractMavenReportRenderer should not depend on Doxia impl classes

**[Konrad Windszus](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=kwin)** opened **[MSHARED-1364](https://issues.apache.org/jira/browse/MSHARED-1364?redirect=false)** and commented

The classes in package `o.a.m.doxia.sink.impl` should by definition not be considered stable API (and therefore only consumed from Doxia classes internally).
However `https://github.com/apache/maven-reporting-impl/blob/72181306bb0e12eed50c4ba4aec98dd76499df39/src/main/java/org/apache/maven/reporting/AbstractMavenReportRenderer.java#L47` depends on some internal constants.
This is dangerous, as those constants were removed in the context of DOXIA-685. Although constants are inlined during compile time, the evaluation of those constants vanished as well, so using them has no longer any effect. Reporting Impl should only rely on stable Doxia API to achieve a better decoupling.

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**Affects:** maven-reporting-impl-4.0.0-M13

Inspect AbstractMavenReportRenderer.java around line 47 and review the Doxia implementation constants it currently uses. Read the stable Doxia API and the DOXIA-685 context first; done means Reporting Impl no longer depends on o.a.m.doxia.sink.impl classes and the project build passes.

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