test: Add Span test

Add a compile-only test that exercises the whole Span API, as template
functions are not fully compile-tested when the file is parsed.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

test/meson.build

@@ -17,6 +17,7 @@ public_tests = [
     ['geometry',                        'geometry.cpp'],
     ['list-cameras',                    'list-cameras.cpp'],
     ['signal',                          'signal.cpp'],
+    ['span',                            'span.cpp'],
 ]
 
 internal_tests = [