Several improvements and cleanups to the Inference system

[oxisto]

This PR does some cleanup and improvements to the inference systems. It is made more configurable, with more options added to InferenceConfiguration.

For example, currently, the Inference class only infers fields. However, some languages (such as C/C++) have global variables, which we can also infer.

Note, that we intentionally NOT infer local variables, since we assume that we have incomplete code, that is probably complete within a function, but not complete in the sense that translation unit files or headers are missing.

This also aligns the DFG of inferred functions more to non-inferred ones and adds inferred methods to the AST.

[konradweiss]

Pls add some small missing documentation and clarify if testGlobals is correct. I also noticed that the check if inference is turned on is fragmented over the subfunctions. while it would be cool to check that asap when the first inference function is called, the checks which inference, e.g. infering records etc. is turned on needs to happen further down so I don't know if we can make it better or have to accept that checking if inference is turned on has to be done in many different places.

[oxisto]

@konradweiss Could you have another look, if the changes are ok please? thanks!

[sonarqubecloud]

Quality Gate passed

The SonarCloud Quality Gate passed, but some issues were introduced.

2 New issues
0 Security Hotspots
84.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud