Deprecate $extensionInfo['mtime'] and ['_info_file_ctime']

Problem/Motivation

Followup from #2959989-20: Deprecate Extension::__call() magic
@andypost:

+++ b/core/lib/Drupal/Core/Extension/ExtensionList.php
@@ -555,7 +555,7 @@ protected function createExtensionInfo(Extension $extension) {
+ $info['mtime'] = $extension->getFileInfo()->getMTime();

we can deprecate this key as it is not parsed see \Drupal\Core\Utility\ProjectInfo::filterProjectInfo() and used only by tests

+++ b/core/lib/Drupal/Core/Utility/ProjectInfo.php
@@ -81,7 +81,7 @@ public function processInfoList(array &$projects, array $list, $project_type, $s
+ $file->info['_info_file_ctime'] = $file->getFileInfo()->getCTime();

consumed only by locale and update modules

and only a handful usages in contrib.

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet

Deprecate $extensionInfo['mtime'] and ['_info_file_ctime'] are deprecated.
Use the $extension object and its methods instead.