MediaWiki 1.38/New configuration system

Config is Data, not code

 * no globals
 * rationale for WMF
 * for DefaultSettings.php
 * for LocalSettings.php
 * for reading config
 * also, use MW_INSTALL_PATH

MainConfigSchema.php replaces DefaultSettings.php
TBD: generated files

TBD: JSON schema style

TBD: loading of defaults

Experimental support for LocalSettings.yaml
TBD: warn about this file being readable from the web

TBD: settings file structure

Caveat: no support for PHP constants

Experimental mode for loading LocalSettings.php

 * most stuff just works (TM)
 * don't use explicit global for reading
 * do use explicit global for writing (really needed?!)
 * be careful about closures

Preview of SettingsBuilder

 * available but unstable
 * use to load settings files
 * use to set/override config programmatically
 * use to load extensions
 * access to defaults, schema

Outlook

 * wmf config overhaul
 * config presets for caching
 * removal of global variables
 * config nodes ideas (vs prefixes and config factory)