EQ_ASSIGN within a nestImplements the relocation of an EQ_ASSIGN and associated tokens
within a nest (nested parse table at one level of nesting).
Note that one assignment expression (such as "a = b = c") can include
multiple assignment operators, an assignment involves just one assignment
operator.
For the relocation of assignment expressions that contain EQ_ASSIGN within
a nest, we need to first find the expressions that contain = and then
split the nest into parse tables each containing one such assignment
expression and then relocate each of them separately.
We can't do all of them together because:
relocate_eq_assign_nest(pd)A parse table.
An assignment can contain more than just three tokens, e.g. (a <- b <- c).
Two assignments can be in the same nest although they don't belong to the same assignment (if-else statement).
Please refer to the section 'Examples' in relocate_eq_assign() for details.