Remove checkstyle warnings from drools core module

[pibizza]

The code in the drools-core module generates a number of checkstyle warnings, related to:

• order of the imports
• use of {}
• use of tabs instead of white spaces
• lack of properly paired hash and equal functions

The relevant code is here. https://github.com/apache/incubator-kie-drools/tree/main/drools-core

[yesamer]

Hi @pibizza, is this task completed?

[pibizza]

No it is not. I am going to leave it here for the moment. If you think it is kind of generating issues I can close this and reopen this later.