Looks like it's needed for the UpdateVarDumps script, so add a note
about that. Also add a type check to the script so that it produces a
clearer error message if it finds an entity with unexpected type.
Bug: T331861
Change-Id: I68f8f954ed754c4282e13599ce06118e2336ecbb
Each generator knows in which situation it is executed, and it
can pass this information to the computer. VariableHolder should
just hold the variables.
Change-Id: I0fb2e01e3e9457cd63948afe2a20439a1c800790