Update CEF to v139, make the necessary changes to the way the media plugin creates cache directories and incorporate a universal build of Dullahan

[callumlinden]

Description

This commit is primarily focused on updating CEF to the latest version (v139 as of August 2025). This is captured in #4498.

Because of significant changes to CEF in the 21 months since was last updated (v118, November 2023) there are additional changes required:

• Prior to CEF 120, each media instance could share a set of cache directories and it worked - mostly. After version 120, this is actively prohibited. Consequently, to update CEF to v139, cache directories are now created with a unique path name.
• Because each instance gets a brand new cache directory and the contents of each is large, the whole cef_cache folder structure is purged at startup (before the parent being created at the first media instance creation)
• The macOS version of CEF has been built historically for the Intel architecture and the magic of Rosetta2 allowed everything to work on Apple Silicon machines. After some update to Chromium (and maybe CEF) that is no longer the case and Intel builds of Chrome, CEF and even the CEF test apps run very slowly on Apple Silicon machines. @RyeMutt's work to create dual architecture (Intel/Arm) builds of CEF and then universal builds of Dullahan are invaluable and once all of the Viewer components are updated to build natively, the Viewer will run very quickly

Known Issues

• The version of CEF in this Viewer is built (by necessity) for the Intel architecture and therefore runs incredibly slowly (unusably so) on Apple Silicon devices. There should be no slowdown running on native Intel hardware. A later phase of this (or another) will facilitate a native ARM build of all Viewer components and this issue will go away.

Checklist

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