[WIP] Move grep from RzCons to RzCore

[XVilka]

Your checklist for this pull request

• I've read the guidelines for contributing to this repository
• I made sure to follow the project's coding style
• I've documented or updated the documentation of every function and struct this PR changes. If not so I've explained why.
• I've added tests that prove my fix is effective or that my feature works (if possible)
• I've updated the rizin book with the relevant information (if needed)

Detailed description

• Move ~ (grep) handling from RzCons to RzCore
• Minor refactoring and cleanup

Test plan

CI is green

Closing issues

Closes #1824
Partially addresses #276

[ret2libc]

I don't remember right now... What is the reasoning to have grep in RzCore and not in RzCons? What are the advantages?

[XVilka]

@ret2libc to make it a part of the syntax and allow nesting, etc.