Who runs it
Microsoft. It names itself with the token bingbot, in a desktop and a mobile version.
What it does
Bing calls it its standard crawler, handling most of its crawling needs each day. It fetches pages for Bing's search index.
Renders JavaScript
Yes. Bing says it regularly updates its rendering engine to the most recent stable version of Microsoft Edge, and that W.X.Y.Z in its user agent is the Edge version it uses.
How to verify it
Run a reverse DNS lookup on the visiting address. The name should end in search.msn.com, and a forward lookup of that name should return the same address. Or match the address against Bing's published list, which Bing says to refresh daily.
robots.txt
Bing says robots.txt files can be configured to tell its crawlers how to interact with your site, and offers a crawl control tool in Bing Webmaster Tools for request rates.
Questions
Does Bingbot run my JavaScript?
Yes. Bing says it renders pages with the most recent stable version of Microsoft Edge.