jshell tool: make all IMPORTS.jsh generated at build time

Like this, but at in the make --


    // Compute all SE imports
    private class AllImports {

        ModuleFinder finder = ModuleFinder.ofSystem();

        Set<ModuleDescriptor> seModules() {
            Set<ModuleDescriptor> closure = new HashSet<>();
            moduleClosure(finder.find("java.se"), closure);
            return closure;
        }

        void moduleClosure(Optional<ModuleReference> omr, Set<ModuleDescriptor> closure) {
            if (omr.isPresent()) {
                ModuleDescriptor mdesc = omr.get().descriptor();
                if (closure.add(mdesc)) {
                    for (ModuleDescriptor.Requires req : mdesc.requires()) {
                        if (!req.modifiers().contains(ModuleDescriptor.Requires.Modifier.STATIC)) {
                            moduleClosure(finder.find(req.name()), closure);
                        }
                    }
                }
            }
        }
        
        Set<String> packages() {
            return seModules().stream().flatMap(md -> md.exports().stream())
                .filter(e -> !e.isQualified()).map(Object::toString).collect(Collectors.toSet());
        }

        String imports() {
            Set<String> si = packages();
            String[] ai = si.toArray(new String[si.size()]);
            Arrays.sort(ai);
            return Arrays.stream(ai)
                    .map(p -> String.format("import %s.*;\n", p))
                    .collect(Collectors.joining());
        }
    }