How to make leaving a PhD program seem like a positive thing on a resume
I think it is a really bad idea to list your time as a grad student as "Researcher".

As a general rule, it's usually considered unwise to make up stuff on a resume, and this includes job titles.  I think the only title that really fits your status is "PhD Student" or "PhD Candidate" (or, if you want to focus on the job, "Teaching Assistant" or "Graduate Research Assistant" or the like - whatever was on your pay stub).

The title of "Researcher" would normally be attached to a full-time (non-student!) staff position, generally someone who works on a research project led by a faculty member.   Although the duties may be somewhat similar, the hiring process and level of responsibility could be rather different, so it is really a misrepresentation for you to claim this title.

Suppose a prospective employer calls your university, checking references, and asks "Was Unsure a Researcher at your institution during the following dates?"  The university is going to answer "No, he/she was a grad student" (or even worse, maybe just "No").  Then the employer tosses your application in the trash because your resume is inaccurate (or as they might say, "falsified").  And if they don't check and you get the job anyway, but they find out later, they could easily consider your application was fraudulent - that gets you fired for sure, and is possibly career ending.

If you think employers are going to figure out anyway that you were in a PhD program, why not just go ahead and put "PhD Candidate" on the resume?