Implement a DDR rewriting for folding the `x[0]` into `*x`, in order
to avoid a useless verbose syntax. Due to concatenation of rewrites, we
will get `&(x[0])` transformed into `x`, which is the rewriting we are
aiming to.
* DecayOp - array or function to pointer decay. Not shown in C.
* BitCastOp - bit-preserving conversion. Emitted as bit_cast if
necessary.
* ExtendOp - zero- or sign-extending conversion from any integer type to
any wider integer type.
* TruncateOp - truncating conversion from any integer type to any
narrower integer type.
* PtrResizeOp - resizes a pointer without changing its pointee type.
Pietro Fezzardi