Allow starting coding agent session from todo comments

[mjbvz]

As a new coding agent entry point, I'd love to be able to start a new session from a TODO comment in my code using a code action. Currently you first have to create an issue to do this

[joshspicer]

Cool idea

[alexr00]

We already have a TODO code action provider, which can create an issue. Might be easy to expand that to include an action to kick off the coding agent.