[mypyc] Record MRO ancestor modules as deps of subclass-defining modules (#21743)

Fixes #21742

Mypy's incremental system only recompiles a module when a recorded
dependency changes, and a dependency edge to an ancestor's module is
created in cases such as an explicit import or a checked expression
whose type references that ancestor. A bare subclass definition produces
neither, so the transitive ancestors never enter the module's dependency
graph.

The goal of this PR is to make the dependency graph reflect what the
generated C actually depends on. When compiling with mypyc, a module
that defines a class now records the modules defining every ancestor in
that class's MRO as indirect dependencies, so an ancestor's interface
change reaches the subclass-defining module directly.