This is an extension of #60507, the reason we have an InternalExecutor interface in sql/sem/tree/eval.go is for use in the builtins package.

Comment from tree/eval.go

// InternalExecutor gives access to an executor to be used for running
// "internal" statements. It may seem bizarre that "expression evaluation" may
// need to run a statement, and yet many builtin functions do it.
// Note that the executor will be "session-bound" - it will inherit session
// variables from a parent session.

This highlights a larger problem that the builtins package is not structured very well. We have both the syntax/function definition as well as some of the business logic inside the builtins package, specifically builtins.go and pg_builtins.go.

Ideally we should split the logic into a separate package and have the builtins package handle plumbing / delegating the logic downstream.

Right now builtins does too much while being in the sem package

cc @ajwerner

Jira issue: CRDB-3179

Epic CRDB-60948