The problem was that under specific circumstances, namely that none
of their children progressed, `GeneratorTracker` will not progress.
This was changed recently, to allow for code like this, where a
`SECTION` follows a `GENERATE` at the same level:

```cpp
SECTION("A") {}
auto a = GENERATE(1, 2);
SECTION("B") {}
```

However, this interacted badly with `SECTION` filters (`-c foo`),
as they could deactivate all `SECTION`s below a generator, and thus
stop it from progressing forever. This commit makes GeneratorTracker
check whether there are any filters active, and if they are, it checks
whether its section-children can ever run.

Fixes #2025

Fixes #2063
Related to #2050

CMake 3.19 introduces new add_test() behavior guarded with the policy
CMP0110.

See: https://cmake.org/cmake/help/latest/policy/CMP0110.html

Update the helper script ParseAndAddCatchTests to consider the policy and
handle the test case name accordingly.

Consistently use 4 spaces instead of tabs

Fix regex that requires two string arguments in the form of
TEST_CASE("a", "b") resulting in not finding TEST_CASE("a") entries.

See https://regex101.com/r/JygOND/1

Fixes: https://github.com/catchorg/Catch2/issues/2055

The problem was that Catch2 did not reliably include `<exception>`
before it checked for the feature test macro for
`std::uncaught_exceptions`. To avoid overhead of including
`<exception>` everywhere, the configuration check was split out
into a separate header.

Closes #2021