Split out pretty-print.c and move pager.c and main-func.h to shared/

This is high-level functionality, and fits better in shared/ (which is for
our executables), than in basic/ (which is also for libraries).

src/shared/id128-print.c

@@ -7,6 +7,7 @@
 #include "alloc-util.h"
 #include "id128-print.h"
 #include "log.h"
+#include "pretty-print.h"
 #include "terminal-util.h"
 
 int id128_pretty_print(sd_id128_t id, bool pretty) {