Use C-style backslash escaping to sanitize non-UTF-8 strings.
The functions are compatible with glib's g_strcompress() and
g_strescape().
The difference is only that g_strescape() escapes all non-printable,
non ASCII character as well, while nm_utils_str_utf8safe_escape()
-- depending on the flags -- preserves valid UTF-8 sequence except
backslash.
The flags allow to optionally escape ASCII control characters and
all non-ASCII (valid UTF-8) characters. But the option to preserve
valid UTF-8 (non-ASCII) characters verbatim, is what distinguishes
from g_strescape().
These functions are only used by nm-meta-setting-desc.c. Make them internal.
Unfortunately, they are part of "common.h" which cannot be used without
the rest of nmcli. Still todo.
The "shared" directory contains files that are possibly used by all components
of NetworkManager repository.
Some of these files are even copied as-is to other projects (VPN plugins, nm-applet)
and used there without modification. Move those files to a separate directory.
By moving them to a common directory, it is clearer that they belong
together. Also, you can easier compare the copied versions to their
original via
$ diff -r ./shared/nm-utils/ /path/to/nm-vpn-plugin/shared/nm-utils/
