This way it is explicit when there is a `StringRef` -> `std::string`
conversion and makes it easier to look for allocations that could
be avoided.
Doing this has already removed one allocation per registered test
case, as there was a completely pointless `StringRef` -> `std::string`
conversion when parsing tags of a test case.
This PR ultimately does 3 things
* Separately tracks matched tests per each filter part (that is, a set of filters separated by an OR (`,`)), which allows Catch2 to report each of the alternative filters that don't match any tests.
* Fixes `-w NoTests` to return non-zero in the process
* Adds tests for `-w NoTests`.
ReusableStringStream holds a std::ostringstream internally, but only exposes the ostream interface.
It caches a pool of ostringstreams in a vector which is currently global, but will be made thread-local.
Altogether this should enable both runtime and compile-time benefits. although more work is needed to realise the compile time opportunities.
