{Aggregate|Density}MeasureComputer: reduce and soften the logging

[ivangalkin]

fixes #1640

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This change is 

[guwirth]

@ivangalkin think it’s possible to filter for the language.

• MeasureComputerContext
  https://github.com/SonarSource/sonarqube/blob/master/sonar-plugin-api/src/main/java/org/sonar/api/ce/measure/MeasureComputer.java has getComponent
• Component
  https://github.com/SonarSource/sonarqube/blob/master/sonar-plugin-api/src/main/java/org/sonar/api/ce/measure/Component.java has FileAttributes and getLanguageKey

So not sure if we can keep some warnings but only for our language?

[ivangalkin]

@guwirth you are right about the FileAttributes::getLanguageKey() property. It's possible to determine the language, but only for FILEs

  /**
   * The attributes of the Component if it's type is File.
   *
   * @throws IllegalStateException if the Component's type is not {@link Type#FILE}
   */
  FileAttributes getFileAttributes();

However the visitor iterates over different component types: the full list is PROJECT, MODULE, DIRECTORY, FILE, VIEW, SUBVIEW. In my opinion it would be too complex (and not really useful) to detect if e.g. MODULE has at least one C/C++ file. It would require manual implementation of recursive algorithm and wouldn't really fit with the visitor approach. Since it's only about the traces, I believe it's not really worth it.

[guwirth]

@ivangalkin ok. Seems there will be anyway some changes: https://jira.sonarsource.com/browse/MMF-365.