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/blockdev-util.h

@@ -0,0 +1,26 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+#pragma once
+
+#include <sys/types.h>
+
+#include "macro.h"
+#include "stdio-util.h"
+#include "string-util.h"
+
+#define SYS_BLOCK_PATH_MAX(suffix)                                      \
+        (STRLEN("/sys/dev/block/") + DECIMAL_STR_MAX(dev_t) + 1 + DECIMAL_STR_MAX(dev_t) + strlen_ptr(suffix))
+#define xsprintf_sys_block_path(buf, suffix, devno)                     \
+        xsprintf(buf, "/sys/dev/block/%u:%u%s", major(devno), minor(devno), strempty(suffix))
+
+int block_get_whole_disk(dev_t d, dev_t *ret);
+int block_get_originating(dev_t d, dev_t *ret);
+
+int get_block_device(const char *path, dev_t *dev);
+
+int get_block_device_harder(const char *path, dev_t *dev);
+
+int lock_whole_block_device(dev_t devt, int operation);
+
+int blockdev_partscan_enabled(int fd);
+
+int path_is_encrypted(const char *path);