Improve no-alias analysis to find arrays-of-arrays

[mppf]

LCALS uses refs to array-of-arrays. Many LCALS kernels could be faster if the Chapel compiler can emit no-alias hints to LLVM optimizations for these refs.

For example:

config const n = 10;

proc kernel(A) {
  // This pattern comes up in LCALS
  ref A1 = A[1];
  ref A2 = A[2];

  for i in 1..n {
    A1[i] = A2[1] + A2[i];
  }
}

proc main() {
  var A:[1..10] [1..10] int;
  kernel(A);
}

Here one might imagine that the compiler can prove that A1 does not alias A2 because:

• A stores sub-arrays by value (not by reference / alias / slice)
• A1 and A2 came from different indices in A

Associated future test: test/analysis/alias/future/ref-to-array-of-arrays.chpl
(added in PR #11779).