Now has keyword-based arguments (old syntax form is still supported).
Discovered tests can have a prefix and/or suffix added to the test names
and the list of discovered tests is available to the caller. The working
dir can also be set and the dependency on the source files is now
optional instead of mandatory.
Extract the `gtest_add_tests` macro from `FindGTest` into a separate
module. GTest or GoogleTest can be used by a project in a several
different ways, including installed libraries in the system, from an
ExternalProject, or adding the GTest source directory as a sub directory
of the project. As not all of these uses are supported by the FindGTest
module the useful `gtest_add_tests` macro is separated to easily enable
reuse.
Issue: #14151
