This is an intermediary collector; it populates an AssetLibraryManager
by creating AssetLibraries and attaching them to AssetCollectors, which
client code can then easily use to populate the produced AssetLibrary.

Previously it was based on Assetic's AssetManager, which did not serve
several of our purposes.

They now implement AssetBagInterface and extend AssetBag. Tests
exercise only the methods not present on AssetBag. TODO - refactor the
dependency logic into a separate interface that can be used here, and
also included as part of AssetInterface.

This has better cross-applicability for different AssetBagInterface
implementations. Also added an isFrozen() checker.

This definitively removes responsibility for sorting from
AssetBagInterface.

Pursuant to #2025649.

providing wider support for typed data definitions within the context configuration. This format will allow us to support constraints in addition to simple typed data definitions.

Created a ContextResolver class to resolve context configurations. Provided basic context configuration storage on the display objects and updated the example display to have a simple string context to demo how contexts can be injected into blocks configured to use them.

made BlockBase extend the Core version of ContextAwarePluginBase instead of the Component version. Also moved the SystemMenuBlock and MenuBlock to be contextually aware of a string that represents the desired active path. This is using a try/catch statement which is really ugly right now. We should refactor it later.

Conflicts:
	core/core.services.yml
	core/lib/Drupal/Core/CoreBundle.php
	core/modules/block/lib/Drupal/block/BlockBase.php
	core/modules/block/lib/Drupal/block/Plugin/Type/BlockManager.php
	core/modules/system/lib/Drupal/system/Plugin/Block/SystemHelpBlock.php
	core/modules/system/lib/Drupal/system/Plugin/Block/SystemMainBlock.php
	core/modules/system/lib/Drupal/system/Plugin/Block/SystemPoweredByBlock.php
	core/modules/tour/tour.module

Issue #1934716 followup by hackwater: [Followup] Merge system.fast_404 config object into system.performance.

Issue #1981292 by aspilicious, pcambra, andypost, swentel: Drop procedural usage of fields in field_sql_storage() & field_ui() tests.

Issue #1981334 by pcambra, aspilicious, swentel, andypost: Drop procedural usage of fields in [n-r] modules.

Issue #1981342 by aspilicious, andypost, swentel: Drop procedural usage of fields in [s-u-v] modules.

Issue #2014037 by hussainweb, kgoel: Replace drupal_container() with Drupal::keyValue() in the update module.

Issue #2009690 by jeroen12345, redfoxxx.ua, InternetDevels, hussainweb: Replace theme() with drupal_render() in user module.

Issue #1981336 by aspilicious, andypost, swentel, amateescu: Drop procedural usage of fields in [t*] modules.

Issue #1981306 by aspilicious, andypost, pcambra, swentel, amateescu: Drop procedural usage of fields in [a-e] modules.

Issue #1981316 by aspilicious, andypost, pcambra, swentel: Drop procedural usage of fields in [f-l] modules.