BE-71: HashQL: Consolidate AST special-form expansion stages into one#8870

indietyp wants to merge 55 commits into

bm/be-481-hashql-lower-null-to-constantunit-during-reificationhashintel/hash:bm/be-481-hashql-lower-null-to-constantunit-during-reificationfrom

bm/be-71-hashql-consider-merging-ast-stageshashintel/hash:bm/be-71-hashql-consider-merging-ast-stagesCopy head branch name to clipboard