keymap: Add back a tiny utility for setting the system keyboard layout

This patch removes the setuid-root flag from the KeyboardSettings GUI
application and adds back the old "keymap" program.

It doesn't feel very safe and sound to have a GUI program runnable
as setuid-root, so in the next patch I'll be making KeyboardSettings
call out to the "keymap" program to do its bidding.

Userland/keymap.cpp

@@ -0,0 +1,35 @@
+#include <LibCore/ArgsParser.h>
+#include <LibKeyboard/CharacterMap.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int main(int argc, char** argv)
+{
+    if (pledge("stdio setkeymap rpath", nullptr) < 0) {
+        perror("pledge");
+        return 1;
+    }
+
+    if (unveil("/res/keymaps", "r") < 0) {
+        perror("unveil");
+        return 1;
+    }
+
+    if (unveil(nullptr, nullptr) < 0) {
+        perror("unveil");
+        return 1;
+    }
+
+    const char* path = nullptr;
+    Core::ArgsParser args_parser;
+    args_parser.add_positional_argument(path, "The mapping file to be used", "file");
+    args_parser.parse(argc, argv);
+
+    Keyboard::CharacterMap character_map(path);
+    int rc = character_map.set_system_map();
+    if (rc != 0)
+        fprintf(stderr, "%s\n", strerror(-rc));
+
+    return rc;
+}