FeaturesManager::getExistingPackages() should limit to the current bundle

Problem/Motivation

FeaturesManager::getExistingPackages() is used to detect existing packages. It is used in two plugins: "existing" and "packages". Both relate to packages for the current bundle.

However, ::getExistingPackages() returns all features modules, regardless of bundle.

Proposed resolution

• Add a $bundle argument to FeaturesManagerInterface::isFeatureModule(), allowing restricting to a given bundle.
• in FeaturesManager:getExistingPackages(), load the current bundle and pass it to ::isFeatureModule().

API changes

New $bundle argument to FeaturesManagerInterface::isFeatureModule(), allowing restricting to a given bundle.