Enable direct execution of tasks in the deno task command using the up/down arrow keys

[kensukesaito]

Currently, the deno task command only displays a list of available tasks. However, it would be even more convenient if we could use the up/down arrow keys to select a task and execute it directly.

$ deno task      
Available tasks:
- dev
    deno serve server.ts
- build
    esbuild index.ts

[dsherret]

It would probably need to be deno task --interactive or something like that.