Python: Fix self-assigned fields and or-expression type propagation

[lshala]

Two related fixes:

• Instance/self-assigned fields (e.g. self.foo = Foo()) were not being declared because self has an UnknownType. This prevented calls on those fields from being resolved.
• There are also cases where the type can either be passed via a parameter or it will be declared with the default constructor (e.g. self.foo = foo or Foo())

Partially fixes #2575

[codecov]

Codecov Report

❌ Patch coverage is 91.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.19%. Comparing base (fedc70a) to head (e3055ff).
⚠️ Report is 2 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...ofer/aisec/cpg/passes/PythonAddDeclarationsPass.kt	60.00%	0 Missing and 2 partials ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
...tlin/de/fraunhofer/aisec/cpg/frontends/Language.kt	85.87% <100.00%> (+0.93%)	⬆️
...cpg/graph/statements/expressions/BinaryOperator.kt	76.36% <100.00%> (+0.43%)	⬆️
...hofer/aisec/cpg/frontends/python/PythonLanguage.kt	94.54% <100.00%> (+0.24%)	⬆️
...ofer/aisec/cpg/passes/PythonAddDeclarationsPass.kt	88.28% <60.00%> (+3.88%)	⬆️

... and 4 files with indirect coverage changes

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[maximiliankaul]

LGTM. Maybe double check with someone more familiar with our assignedTypes functionality.