webm/theora/yuv2rgb: Fix YUV conversion issues and add BGRP WEBM handling. (Now clang-format friendly.)

This should fix the various issues with colours in Ogg Theora and WEBM playback.
(A reference project is attached to PR #26051, which this commit should be part of.)

This version of the commit, rather than moving x->RGBA handling into libsimplewebm, uses a colourspace field added to libsimplewebm by a PR there.
Thus, the commit that precedes this should be the synchronization & cleanup commit for that.

Also, this version is now clang-format friendly. I hope.

This is to get the colourspace information commit in,
 but it also performs a bit of cleanup regarding the entry in the thirdparty README.

The reason libwebm wasn't synced is because it has a bunch of unmarked changes,
 and it'd be better if the person responsible untangled that as
 they may know what they did and why they did it.

Given this, it might be a good idea to disconnect libwebm from the libsimplewebm code.

Add gcc-8 to Travis.

Fix project opening while filter is applied.

C#: Throw ObjectDisposedException from disposed wrapper classes

C#: Add random functions to GD class

Fixes #25268

Fix warnings seen with warnings=all and recent GCC 8.2.

Allowing setting particles lifetime greater than 600

C#: fix Quat.Equals.

Fixed area collision report with concave

Add hex-encoded version number to Engine singleton for easy comparisons

Make direct casting among Error and godot_error enums (#23015).

Added shadow_color property to gles2

Added support to scale areas, fixes #23448

Auto-cleanup missing addons

Fix description size in "New Node" dialog

Fix AudioStreams::stop possibly causing a small noise

Small improvements to the Resource doc