basic,shared: move a bunch of files to src/shared/

The goal is to move everything that requires selinux or smack
away from src/basic/. This means that src/basic/label.[ch] must move,
which implies btrfs-util.[ch], copy.[ch], and a bunch of other files
which form a cluster of internal use.

This is just moving text around, so there should be no functional difference.

test-blockdev-util is new, because path_is_encrypted() is moved to
blockdev-util.c, and so far we didn't have any tests for code there.

src/shared/mkdir-label.c

@@ -0,0 +1,59 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <stdio.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include "label.h"
+#include "macro.h"
+#include "mkdir.h"
+#include "selinux-util.h"
+#include "smack-util.h"
+#include "user-util.h"
+
+int mkdir_label(const char *path, mode_t mode) {
+        int r;
+
+        assert(path);
+
+        r = mac_selinux_create_file_prepare(path, S_IFDIR);
+        if (r < 0)
+                return r;
+
+        r = mkdir_errno_wrapper(path, mode);
+        mac_selinux_create_file_clear();
+        if (r < 0)
+                return r;
+
+        return mac_smack_fix(path, 0);
+}
+
+int mkdirat_label(int dirfd, const char *path, mode_t mode) {
+        int r;
+
+        assert(path);
+
+        r = mac_selinux_create_file_prepare_at(dirfd, path, S_IFDIR);
+        if (r < 0)
+                return r;
+
+        r = mkdirat_errno_wrapper(dirfd, path, mode);
+        mac_selinux_create_file_clear();
+        if (r < 0)
+                return r;
+
+        return mac_smack_fix_at(dirfd, path, 0);
+}
+
+int mkdir_safe_label(const char *path, mode_t mode, uid_t uid, gid_t gid, MkdirFlags flags) {
+        return mkdir_safe_internal(path, mode, uid, gid, flags, mkdir_label);
+}
+
+int mkdir_parents_label(const char *path, mode_t mode) {
+        return mkdir_parents_internal(NULL, path, mode, UID_INVALID, UID_INVALID, 0, mkdir_label);
+}
+
+int mkdir_p_label(const char *path, mode_t mode) {
+        return mkdir_p_internal(NULL, path, mode, UID_INVALID, UID_INVALID, 0, mkdir_label);
+}