[php2cpg] Change method and call representation to fix dataflow through lambdas

[johannescoetzee]

TODOs left to get this out of draft status:

• Update methodFullNames/typeFullNames for the synthetic method types by prefixing the filename or such to avoid duplicate type full names. For some reason just adding this prefix in the createAndPushMethodTypeDecl method breaks stuff, but I probably just missed a case.
• Fix remaining unit tests
• Decide what we want to do about the PhpTypeRecoveryPass