Investigate replacing push + static call with tail calls in implicit closure functions

[sstrickl]

After CL 166622 lands for #40813, implicit closure functions no longer perform any internal checking. Instead, they are purely a redirect to the target.

Determine whether there is any value to having frames for implicit closure functions separate from their target. If not, in a followup CL change FlowGraphBuilder::BuildGraphOfImplicitClosureFunction to instead replace the closure on the stack with the receiver for a dynamic target, or adjust the arguments on the stack as necessary for a static target, and perform a tail call.

/cc @mkustermann