Deprecated method invocations on non-type-hinted objects are not detected

Problem/Motivation

There are many places where contrib could be invoking methods on objects whose type is unknown to static analysis. Per #3096959-29: Drupal 9 deprecated code report, an example of this (from the Crop API module) is:

$scheme = \Drupal::service('file_system')->uriScheme($uri);

Because the @return of \Drupal::service() is documented simply as "mixed", PHPStan does not know what class/interface uriScheme() is being called on, and therefore can't determine whether it's deprecated.

As a result, it does not report a deprecation error, when in fact there is one. Failing to report these means contrib modules that pass Upgrade Status will still fail to work on Drupal 9.

Proposed resolution

What if we commit a file to the codebase of Upgrade Status that contains an index of all of core's method names (across all classes), and for each method name, which interfaces/classes define it. Note that this information is already determined for generating api.drupal.org, so perhaps we can leverage whatever code generates that to also generate this index file?

Then, can we add code to the PHPStan process that detects when a method is being called on an object of unknown type, and for those cases, looks up the method from this index file to determine the possible classes it might be getting called on. And, if the method is deprecated in at least one of these classes, then flag it as a potential deprecation error.

While this could lead to false positives (if it's a method name that's deprecated in one interface/class but not in another), that's preferable to false negatives, and the false positive can be fixed by adding the correct typehint to the flagged code.

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet