[Lens] Use fork of expression service

[timroes]

The expression service does now support forking. We should fork it inside Lens, and then register our lens specific functions on that fork (which can be used inside the editor and inside the embeddable), so we won't pollute Canvas autocompletion with the Lens internal expressions for now.

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)

[timroes]

Blocked by #59744

[flash1293]

@ppisljar is this still up to date? Should Lens use forking to hide the internal functions? AFAIK this will be solved with tags instead, right?

[ppisljar]

yes lets close this one, we will work on either tag or flag to do this.