Create SootClass builder

[wkktoria]

As described in #1059, I've created a builder for SootClass which is based on SootMethod and SootField's builders.

[swissiety]

thanks for your contribution! If you like to, we would really appreciate if you could do the same for the OverridingClassSource / OverridingMethodSource so SootUp can have a testcase demonstrating the usage.

[wkktoria]

Sure, I'll work on making changes to these as well.

[swissiety]

Thank you! As we want to create a complete OverridingClassSource making use of multiple methods at once please return the different interfaces (as an accumulated interface/step) from the with* methods (e.g. see https://www.svlada.com/step-builder-pattern/).
(applies to both of the added Builders)

We even could think about extending the API of withMethods(Set )/ withFields(Set) methods to singular withField(SootField) and collect the parameters on our own.

[wkktoria]

I've changed the builders to use different interfaces as suggested, but I am not sure how to replace these methods with singular one.