If someone gives me notes, feedback, or ideas during the development of my script, are they entitled to credit?

In short, no, that person is not inherently entitled to any credit, especially if his contribution was just notes or feedback.

If that person came up with the idea for the screenplay, he is still not entitled to credit. Much in the way ideas are not copyrightable but screenplays are, it is the execution of the idea that’s worthy of credit — the actual “work of writing.” There are extreme cases where “idea by” or “based on an idea by” can be granted, but it is very rare.

Ultimately, it is up to the studio to submit the writing credits, and up to the writers to call for arbitration. So while it may be rare for the WGA to grant an “idea by” credit, in theory a studio could submit that credit and have it stick if no one challenges it.