Not fully happy about the way this one interacts with the various
platforms. Maybe the platform_config.h should be generated by the
SCsub instead of passing a define just to know where is the header.

Sources are untouched, tarball from https://sourceforge.net/projects/libsquish

Same rationale as the previous commits.

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.

Same rationale as the previous commits.

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.

Note that there are two Godot-specific changes made to libwebp
for the javascript/HTML5 platform. They are documented in the
README.md.

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 :)

Building against shared libraries only implemented for Linux X11 so far.
TODO: Document Godot's modifications of upstream enet.

Similar rationale as in previous commit.

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.

Drop nedmalloc which is apparently not used anymore

Add "button_selected" signal to ButtonGroup

Remove speex support, it is obsoleted by opus

Fix #6803 - Particle2D params

Re-Allow absolute paths, make them behave correctly

Replace a node with saved branch scene instance

Allow turning off zero-padding for line numbers

As mentioned by upstream, Xiph.Org [0]:
> The Speex codec has been obsoleted by Opus. It will continue to be
> available, but since Opus is better than Speex in all aspects,
> users are encouraged to switch.

[0] http://www.speex.org/

Adapt overlooked instances of zero-based column numbers

Fix GraphEdit connection wire when zoom in/out

Only show AnimationEditor automatically when an Animplayer is selected.

New load icon, removed unused open icon

Expose resizable property of GraphNode in inspector

Previous behaviour was to show it when an AnimationPlayer has been detected in the scene, now you actually have to select it.
Fixes #6213

This give a proper fix for #4280 - #3106 , allowing absolute paths
that starts from the file system, not the resource folder

Also closes: #6801

This reverts commit e59820ac.

Refresh TextureRegionEditor when region has been changed externally.