[llvm] ConstraintSystem: replace data structure with Matrix (PR #98895)

[Ramkumar Ramachandra via llvm-commits]

artagnon wrote:

The LLVM Compile Time Tracker results are in, and they look good: https://llvm-compile-time-tracker.com/compare.php?from=17844494b4ea0bc465fc31b745a537b9367d6608&to=b1c870b25bb7fa20a17362f3e14557830bb31ff2&stat=instructions:u.

https://github.com/llvm/llvm-project/pull/98895