Fix potential infinite loops in generators combined with section filter

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

src/catch2/internal/catch_test_case_tracker.hpp

@@ -173,6 +173,10 @@ namespace TestCaseTracking {
 
         void addInitialFilters( std::vector<std::string> const& filters );
         void addNextFilters( std::vector<std::string> const& filters );
+        //! Returns filters active in this tracker
+        std::vector<std::string> const& getFilters() const;
+        //! Returns whitespace-trimmed name of the tracked section
+        std::string const& trimmedName() const;
     };
 
 } // namespace TestCaseTracking