types for `invoke_task`

[ryanatkn]

One of the few rough edges I notice often in Gro these days is the lack of types for invoke_task.

• generate types so task name string+params are checked against the project's tasks and their args (resolve all including gro's builtins)
  • maybe import task types using the same strategy as SvelteKit, tsconfig rootDirs with ./$types.js?
• maybe invoke_task should optionally accept a task function reference? the string form allows you to transparently override builtins which I continue to like