and add NM_IN_SET*_TYPED() macros, which allow to explicitly select
the type of "x".

_NM_GET_PRIVATE() macro is used to implement a standard private-getter, but it
requires that "self" is a pointer of either "const type *" or "type *". That
is great in most cases, but sometimes we have predominatly self pointers of
different type, so it would require a lot of casts.

Add a different form _NM_GET_PRIVATE_VOID() where self pointer can be any
non-const pointer and returns a non-const private pointer after casting.

Add utility functions to check the value of a route attribute.

Use a consistent order of "static inline". This seems the prefered
order in general, and we also use it more often already.

- simplify nm_strquote_a().

- use '"' for quoting instad of '\''.

- have nm_sprintf_bufa() evalute @n_elements only once.

I think NM_CACHED_QUARK_FCN() is better because:

- the implementation is in our hand, meaning it is clear that
  putting a "static" before NM_CACHED_QUARK_FCN() is guaranteed to
  work -- without relying on G_DEFINE_QUARK() to be defined in a way
  that this works (in fact, we currently never do that and instead
  make all functions non-static).
- it does not construct function names by appending "_quark".
  Thus you can grep for the entire function name and finding
  the place where it is implemented.
- same with the stings, where the new macro doesn't stringify the
  argument, which is less surpising. Again, now you can grep
  for the string including the double quoting.

(yes, I really use grep to understand the source-code)

NM_CACHED_QUARK_FCN() is a replacement for G_DEFINE_QUARK().
G_DEFINE_QUARK() is mostly used to define GError quarks. As
such, it always appends _quark() to the function name, which
is unfavorable because it makes it harder to grep for the
definition of the function.

In general I think that macros that defined symbols by concatenating
something should be avoided because that makes it harder to locate
where the symbol was defined.

Fix it by converting the macro to an inline function. It's anyway
nicer.

    $ make src/src_libNetworkManagerBase_la-main-utils.lo
      CC       src/src_libNetworkManagerBase_la-main-utils.lo
    In file included from ./shared/nm-utils/nm-macros-internal.h:29:0,
                     from ./shared/nm-default.h:178,
                     from src/main-utils.c:22:
    src/main-utils.c: In function ‘nm_main_utils_setup_signals’:
    ./shared/nm-utils/nm-glib.h:144:36: error: comparison of unsigned expression >= 0 is always true [-Werror=type-limits]
                  && glib_micro_version >= (micro))))
                                        ^
    src/main-utils.c:82:6: note: in expansion of macro ‘nm_glib_check_version’
      if (nm_glib_check_version (2, 36, 0)) {
          ^~~~~~~~~~~~~~~~~~~~~
    cc1: all warnings being treated as errors
    Makefile:12312: recipe for target 'src/src_libNetworkManagerBase_la-main-utils.lo' failed