[Tolk] Change order of assignment evaluation, lhs first

In FunC (and in Tolk before), the assignment
> lhs = rhs
evaluation order (at IR level) was "rhs first, lhs second".
In practice, this did not matter, because lhs could only
be a primitive:
> (v1, v2) = getValue()
Left side of assignment actually has no "evaluation".
Since Tolk implemented indexed access, there could be
> getTensor().0 = getValue()
or (in the future)
> getObject().field = getValue()
where evaluation order becomes significant.

Now evaluation order will be to "lhs first, rhs second"
(more expected from user's point of view), which will become
significant when building control flow graph.

tolk-tester/tests/allow_post_modification.tolk

@@ -147,5 +147,5 @@ fun main() {
     // x.0 x.1
 """
 
-@code_hash 7627024945492125068389905298530400936797031708759561372406088054030801992712
+@code_hash 61280273714870328160131559159866470128402169974050439159015534193532598351244
 */