Moved matcher-based capture macros into their own file

- this file excluded from the CATCH_CONFIG_DISABLE_MATCHERS path.
- matchers are always compiled in to the impl file
- _THROWS_WITH macros are still available with matchers disabled - but only the ones that take a string
- tests that use matchers have #ifdefs, so the whole SelfTest project can compile with matchers disable.

include/internal/catch_assertionhandler.h

@@ -10,7 +10,6 @@
 
 #include "catch_decomposer.h"
 #include "catch_assertioninfo.h"
-#include "catch_matchers_string.h" // !TBD: for exception matchers
 
 namespace Catch {
 
@@ -67,9 +66,6 @@ namespace Catch {
         void unsetExceptionGuard();
     };
 
-    using StringMatcher = Matchers::Impl::MatcherBase<std::string>;
-
-    void handleExceptionMatchExpr( AssertionHandler& handler, StringMatcher const& matcher, StringRef matcherString  );
     void handleExceptionMatchExpr( AssertionHandler& handler, std::string const& str, StringRef matcherString );
 
 } // namespace Catch