Classes will automatically inherit the virtual-ness of their base
class destructors. If the base class already has a virtual
destructor and the derived class needs default destructor semantics
then the derived class can omit defining the destructor in favor of
the compiler automatically defining it.

This has an additional benefit of reenabling move semantics. The
presence of a user-specified destructor automatically disables move
operations.

Closes #2746 

---------

Co-authored-by: Holger Kaelberer <Holger.Kaelberer@bmw.de>

This PR fixes the handling of semicolon and backslash characters in test names in the CMake test discovery

Closes #2674 

Introducing a new DISCOVERY_MODE mode option, which provides greater
control over when catch_discover_tests perforsm test discovery.

It has two supported modes:
* POST_BUILD: The default behavior, which adds a POST_BUILD command
  to perform test discovery after the test has been built as was
  always done so far.

* PRE_TEST: New mode, which delays test discovery until test execution.
  The generated include file generates the appropriate CTest files at
  runtime and regenerates the CTest files when the executable is
  updated.
  This mode can be used in build-environments that don't allow for
  executing the linked binaries at build-time (like in a
  cross-compilation environment).

DISCOVERY_MODE can be controlled in two ways:
1. Setting the DISCOVERY_MODE when calling catch_discover_tests.

2. Setting the global CMAKE_CATCH_DISCOVER_TESTS_DISCOVERY_MODE prior
   to calling gtest_discover_tests.

Closes #2493

Move test discovery logic into new catch_discover_tests_impl method
and make CatchAddTests aware of whether it is being launched in
CMake's script mode.

When launched in script mode, catch_discover_tests_impl is called
passing arguments obtained from the definitions passed into the call
to cmake. This preserves the existing behavior assumed by Catch.cmake.

Looking ahead, it also allows CatchAddTests to be included in
generated files and call catch_discover_tests_impl to perform test
discovery at test runtime with the new PRE_TEST discovery mode
introduced later.