Move specialized execute method code into an external phase (#51954)

This change moves almost all of the customized code required to decorate 
the execute method into an external phase. This external phase operates 
only on the ir tree after the user tree has generated the initial ir tree from 
user specified code. The external phase uses ir nodes to create the 
necessary customized code instead of writing asm directly. This is a first 
example of modifying the ir tree to customize it specifically for Elasticsearch 
and leaves the ir nodes in a more generic state.

Another change required for this was to remove the notion of auto-return 
from the ir tree completely. The user tree is now responsible for generating 
appropriate ir tree nodes to support auto-return. This is the first example of 
divergent user and ir trees as the user tree is intended to be higher level 
while the ir tree is supposed to provide lower level translation into asm.

Relates to #49869
Relates to #51841