util-lib: split out all temporary file related calls into tmpfiles-util.c

This splits out a bunch of functions from fileio.c that have to do with
temporary files. Simply to make the header files a bit shorter, and to
group things more nicely.

No code changes, just some rearranging of source files.

src/fuzz/fuzz-catalog.c

@@ -2,9 +2,9 @@
 
 #include "catalog.h"
 #include "fd-util.h"
-#include "fileio.h"
 #include "fs-util.h"
 #include "fuzz.h"
+#include "tmpfile-util.h"
 
 int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
         _cleanup_(unlink_tempfilep) char name[] = "/tmp/fuzz-catalog.XXXXXX";

src/fuzz/fuzz-journald-native-fd.c

@@ -1,13 +1,13 @@
 /* SPDX-License-Identifier: LGPL-2.1+ */
 
 #include "fd-util.h"
-#include "fileio.h"
 #include "fs-util.h"
-#include "fuzz.h"
 #include "fuzz-journald.h"
+#include "fuzz.h"
 #include "journald-native.h"
 #include "memfd-util.h"
 #include "process-util.h"
+#include "tmpfile-util.h"
 
 int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
         Server s;