Make the V8-related code lldb-agnostic

[mmarchini]

Most of the code we have on llnode doesn't have to be tied to lldb. We use lldb entirely for memory access (either on a core dump or living process). If we separate the code, providing an interface that can be implemented, we could provide multiple backends for llnode. For example, we could keep the lldb build and provide a smaller build in Webassembly using libelf and our own REPL to read the core dump (this would improve installation for users quite a bit).

[mmarchini]

Not looking into this anymore, and since there wasn't much interest I'll close this. Doesn't mean we can't continue refactoring to accomplish this.