set test command to target name instead of the test name if a target is given
If a test is specified by a
TARGET and a
NAME is given like
add_executable(foo source.cc) add_dune_all_flags(foo) dune_add_test(NAME bar TARGET foo)
the name is taken as the command.
This MR changes this such that the executable name of the target is takes as default for the comment. It also adjusts the documentation.