[!!!][FEATURE] Move extension configuration to install tool

With #82254 LocalConfiguration serialized array EXT/extConf has been
changed to a not serialized array in EXTENSIONS. This patch follows
up on this task an finishes various tasks:

* An install tool silent upgrader upmerges given EXT/extConf settings
  to EXTENSIONS array. The resulting EXTENSIONS array does not contain
  dots for sub paths in its array key anymore and is accessible with a
  new ExtensionConfiguration->get() API to fetch values and whole
  extension config.
* A new API is introduced to get() and set() extension specific
  configuration, is documented and used throughout the core to not
  unserialize old EXT/extConf anymore. Setting values updates legacy
  EXT/extConf to new values including compatible 'dot' ending on
  nested array configurations.
* If extensions come with new configuration items in ext_conf_template.txt
  a silent upgrader of the install tool synchronizes these to the
  EXTENSIONS and old extConf array. Extension authors can rely on that
  and always fetch new keys from the new ExtensionConfiguration->get()
  API right away. The synchronization is also triggered when new
  extensions are loaded or extensions are updated via the extension
  manager.
* Core usages are adapted to the new API.
* Next to the main get() / set() API, the extension configuration
  form is extracted from the extension manager and put into the install
  tool as a new card in "Settings". The code below is streamlined
  and encapsulated with just a couple of public methods in class
  'ExtensionConfigurationService' as internal class for use in install
  tool and extension manager.

Resolves: #82368
Related: #82254
Releases: master
Change-Id: I88568fa355f8f6fd5acc9850dcdd718fdd9a1b2e
Reviewed-on: https://review.typo3.org/54034


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Daniel Gorges <daniel.gorges@b13.de>
Tested-by: Daniel Gorges <daniel.gorges@b13.de>
Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>