Symbol resolver with EOG power

[oxisto]

This PR leverages the power of the already established EOG to establish a relatively good order of resolving symbols. This may not be 100 % accurate yet, but gives us a good enough approximation for now.

In this PR, we also merged the VariableUsageResolver and FunctionCallResolver into a single SymbolResolver. The code is mostly copy/paste from both resolvers and still has a lot of potential for more refactoring in the future, because both did similar things.

The resolver will look for EOGStartHolder nodes (a new interface), to start the resolving cycle. Examples include function declarations, top-level declarations or catch-clauses of try-statements. After gathering all start nodes, it will follow the EOG edges and resolve variables and functions, depending on the type of node it encounters.

This allows us to resolve scenarios where a variable's type depends on the outcome of a function call and then a method call is called on it (which was not possible to resolve before), like the following:

var variable = method();
variable.method2();

It also slightly improves symbol resolving in the individual languages, primarily Go, by modelling more language specifics, such as built-in functions or type derivation logic.

[konradweiss]

Some minor changes, and an idea for how to document and change a Todo in code. I did also ask some questions to help me understand some things that are unclear to me.

[oxisto]

We also need to update https://fraunhofer-aisec.github.io/cpg/CPG/specs/eog/#variabledeclaration because the EOG of variable declarations changed.

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

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90.6% Coverage
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