Took the opportunity to undo the Godot changed made to the
opus source. The opus module should eventually be built in its
own environment to avoid polluting others with too many include
dirs and defines.
TODO: Fix the platform/ stuff for opus.
(cherry picked from commit d9a291f641)
speex module was only added while cherry-picking, as speex is removed
in the master branch but we don't want to break compatibility in 2.1.x.
Unbundling wasn't done as the module uses the internal speex_free,
so it would require some more work.
Note that there are two Godot-specific changes made to libwebp
for the javascript/HTML5 platform. They are documented in the
README.md.
(cherry picked from commit ee3cf211c6)
They are not particularly packaged in Linux distros so we do not
facilitate unbundling via SCons. There could be done if/when there
is interest.
Also s/pnm/pbm/, long-lived typo :)
(cherry picked from commit b1e8889d96)
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.
(cherry picked from commit 5fef84a135)
