Unify and refactor value printing

Previously, there were two mostly-identical value printers -- one in
`libexpr/eval.cc` (which didn't force values) and one in
`libcmd/repl.cc` (which did force values and also printed ANSI color
codes).

This PR unifies both of these printers into `print.cc` and provides a
`PrintOptions` struct for controlling the output, which allows for
toggling whether values are forced, whether repeated values are tracked,
and whether ANSI color codes are displayed.

Additionally, `PrintOptions` allows tuning the maximum number of
attributes, list items, and bytes in a string that will be displayed;
this makes it ideal for contexts where printing too much output (e.g.
all of Nixpkgs) is distracting. (As requested by @roberth in
https://github.com/NixOS/nix/pull/9554#issuecomment-1845095735)

Please read the tests for example output.

Future work:
- It would be nice to provide this function as a builtin, perhaps
  `builtins.toStringDebug` -- a printing function that never fails would
  be useful when debugging Nix code.
- It would be nice to support customizing `PrintOptions` members on the
  command line, e.g. `--option to-string-max-attrs 1000`.

src/nix-env/user-env.cc

@@ -8,6 +8,8 @@
 #include "eval.hh"
 #include "eval-inline.hh"
 #include "profiles.hh"
+#include "print-ambiguous.hh"
+#include <limits>
 
 
 namespace nix {
@@ -106,7 +108,8 @@ bool createUserEnv(EvalState & state, DrvInfos & elems,
        environment. */
     auto manifestFile = ({
         std::ostringstream str;
-        manifest.print(state.symbols, str, true);
+        std::set<const void *> seen;
+        printAmbiguous(manifest, state.symbols, str, &seen, std::numeric_limits<int>::max());
         // TODO with C++20 we can use str.view() instead and avoid copy.
         std::string str2 = str.str();
         StringSource source { str2 };