draft: lcov: 2.1

[GitMensch]

still needs adjustments to the patches, which are likely to be a complete rewrite in parts...
supersedes #20546.

From the LCOV release notes:

Changes in version 2.0 include:

• Support for differential coverage analysis
• Support for annotation of reports with date and owner information ("binning")
• Support for data filtering to remove artifacts such as exception branches
• Improved HTML navigation and display features
• Improved performance via parallelism
• Improved error checking and error management.

Additional changes in version 2.1 include:

• Support for other languages/data import from other tools - Perl and Python, in particular, as well as XML import - e.g., from cobertura.
  See perl2lcov --help, py2lcov --help, and xml2lcov --help - as well as the associated tests.
• Improved callback support. See the discussion in the genhtml man page.
• Improved error checking
• lcov regression test suite added to the release - see $LCOV_HOME/share/lcov/tests/README.md for directions on how to execute them in your environment.
• Use lcov to generate coverage reports for lcov - see the directions, above for how to run the lcov regressions and generate a coverage report.
• Bug fixes.