Add --copy-file-range option to pg_upgrade.

The copy_file_range() system call is available on at least Linux and
FreeBSD, and asks the kernel to use efficient ways to copy ranges of a
file.  Options available to the kernel include sharing block ranges
(similar to --clone mode), and pushing down block copies to the storage
layer.

For automated testing, see PG_TEST_PG_UPGRADE_MODE.  (Perhaps in a later
commit we could consider setting this mode for one of the CI targets.)

Reviewed-by: Peter Eisentraut <peter@eisentraut.org>
Discussion: https://postgr.es/m/CA%2BhUKGKe7Hb0-UNih8VD5UNZy5-ojxFb3Pr3xSBBL8qj2M2%3DdQ%40mail.gmail.com

meson.build

@@ -2420,6 +2420,7 @@ func_checks = [
   ['backtrace_symbols', {'dependencies': [execinfo_dep]}],
   ['clock_gettime', {'dependencies': [rt_dep], 'define': false}],
   ['copyfile'],
+  ['copy_file_range'],
   # gcc/clang's sanitizer helper library provides dlopen but not dlsym, thus
   # when enabling asan the dlopen check doesn't notice that -ldl is actually
   # required. Just checking for dlsym() ought to suffice.