Update base for Update on "[compiler] Introduce OutlinedFunctionExpression HIR"

This is very similar to the existing FunctionExpression HIR node
intentionally, so that we can share all the infra between them.

There's a new `outlinedFunc` field on this that will hold the newly
created function that needs to be compiled outside the function body.

The `loweredFunc` will hold the updated HIR for rendering the
outlinedFunc in the callback.

[ghstack-poisoned]