Newly installed versions of the engine will now attempt to copy the project-agnostic config settings from a previous engine installation. This happens by way of a versioned manifest that copies old versions when the manifest does not exist, or is a different version. This code path is benign for non-installed versions of the engine (or FPaths::ShouldSaveToUserDir() is false).
EditorGameAgnosticSettings and EditorUserSettings ini paths have been renamed to EditorSettings and EditorPerProjectUserSettings respectively to better convey their purpose. In general, most settings should be saved in EditorSettings (project-agnostic) so that they apply regardless of which project is open. We have some way to go migrating existing settings for this to be the case, however.
Some previously per-project configuration files are now project-agnostic (such as Editor.ini, EditorKeyBindings.ini, and EditorLayout.ini)
GEditor->Access...Settings and GEditor->Get...Settings have been removed in favor of direct access of the CDO through GetMutableDefault<> and GetDefault<> respectively. Global config ini filenames that are not set up are now neither loaded nor saved on build machines, to handle the problem of indeterminate state more generically.
This addresses UETOOL-270 (Most editor preferences should be project-agnostic)
[CL 2517558 by Andrew Rodham in Main branch]
