Pass the whole IStream wrapper into reporter

This will become useful when reworking colour support, because
Win32 colour support requires checking whether the output is
stdout, which is done through the `IStream` wrapper.

src/catch2/internal/catch_console_colour.cpp

@@ -160,7 +160,7 @@ namespace {
         void setColour( const char* _escapeCode ) {
             // The escape sequence must be flushed to console, otherwise if
             // stdin and stderr are intermixed, we'd get accidentally coloured output.
-            getCurrentContext().getConfig()->defaultStream()
+            getCurrentContext().getConfig()->defaultStream()->stream()
                 << '\033' << _escapeCode << std::flush;
         }
     };