The reordering of the SConscript includes allows to ensure that
stuff like the builtin zlib headers will be available for libpng.
Also moved glew back into global env, otherwise windows seems
not to find it... Kind of shooting in the dark with this multi-env
setup.
This allows to pass include paths and flags only to a given thirdparty
library, thus preventing conflicts between their files (e.g. between
opus and openssl which both provide modes.h.
This also has the nice effect of making the compilation command smaller
for each module as it no longer related to all other modules, only the
final linking brings them together.
This however requires adding manually the ogg include path in opus
and vorbis when building against the builtin ogg, since it is no longer
in the global env.
Also simplified template 'thirdparty_<module>_sources' to
'thirdparty_sources'.
"Core" modules like cscript, gdscript, gridmap, ik and virtual_script
still use the main env_modules, but it could be changed if need be.
Uses the new structure agreed upon in #6157, but the thirdparty/ folder
does not behave following a logic similar to that of modules/ yet.
The png driver can't be moved to a module as discussed in #6157, as it's
required by core together with a few other ImageLoader implementations
(see drivers/register_driver_types.cpp:register_core_driver_types())
Dropped the possibility to disable PNG support, it's a core component
of Godot.
