Move-enable various parts of TextFlow

This removes about 200 pointless copies from printing the help
message (the original motivation for the change), and also nicely
improves performance of the various reporters that depend on
TextFlow.

src/catch2/internal/catch_clara.cpp

@@ -366,8 +366,8 @@ namespace Catch {
 
             optWidth = ( std::min )( optWidth, consoleWidth / 2 );
 
-            for ( auto const& cols : rows ) {
-                auto row = TextFlow::Column( cols.left )
+            for ( auto& cols : rows ) {
+                auto row = TextFlow::Column( CATCH_MOVE(cols.left) )
                                .width( optWidth )
                                .indent( 2 ) +
                            TextFlow::Spacer( 4 ) +