Userland: Add a very simple hexdump program :^)

This can definitely be improved, but it does the basic job!

Userland/hexdump.cpp

@@ -0,0 +1,69 @@
+#include <AK/LogStream.h>
+#include <LibCore/ArgsParser.h>
+#include <LibCore/File.h>
+#include <ctype.h>
+
+int main(int argc, char** argv)
+{
+    Core::ArgsParser args_parser;
+    const char* path = nullptr;
+    args_parser.add_positional_argument(path, "Input", "input", Core::ArgsParser::Required::No);
+
+    args_parser.parse(argc, argv);
+
+    RefPtr<Core::File> file;
+
+    if (!path) {
+        file = Core::File::construct();
+        bool success = file->open(STDIN_FILENO, Core::File::ReadOnly, Core::File::ShouldCloseFileDescription::No);
+        ASSERT(success);
+    } else {
+        auto file_or_error = Core::File::open(path, Core::File::ReadOnly);
+        if (file_or_error.is_error()) {
+            warnln("Failed to open {}: {}", path, file_or_error.error());
+            return 1;
+        }
+        file = file_or_error.value();
+    }
+
+    auto contents = file->read_all();
+
+    Vector<u8, 16> line;
+
+    auto print_line = [&] {
+        for (size_t i = 0; i < 16; ++i) {
+            if (i < line.size())
+                printf("%02x ", line[i]);
+            else
+                printf("   ");
+
+            if (i == 7)
+                printf("  ");
+        }
+
+        printf("  ");
+
+        for (size_t i = 0; i < 16; ++i) {
+            if (i < line.size() && isprint(line[i]))
+                putchar(line[i]);
+            else
+                putchar(' ');
+        }
+
+        putchar('\n');
+    };
+
+    for (size_t i = 0; i < contents.size(); ++i) {
+        line.append(contents[i]);
+
+        if (line.size() == 16) {
+            print_line();
+            line.clear();
+        }
+    }
+
+    if (!line.is_empty())
+        print_line();
+
+    return 0;
+}