Deep updates in F* blows up memory.

[karthikbhargavan]

We do not have a small reproducer, but deep updates in F* are causing a memory blow up.

Two of these patterns are:

• a.coefficients[i] += 3
• a[i][j] += 3

These are translated into nested updates (which is correct) but chaining two such updates already uses up gigabytes of memory when typechecking with F* and adding more updates cases OOM errors in F*.