Loop Invariant Code Motion (LICM)

LICM is a standard pass that movies computations that are independent of loop iterations to outside of the loop, so that they aren't executed on each iteration (they need not be).

This requires
1. [IR infrastructure of representing loop constructs](https://github.com/FuelLabs/sway/issues/5368).
3. Run-time gas measurements for impact measurement. The motion is more-or-less code-size neutral.

Parent Issue: #2383

Start by reading the prerequisite IR loop infrastructure issue #5368 and the parent issue #2383 to understand the compiler context for LICM. Done means adding the loop-invariant code-motion pass after loop constructs are representable and measuring its runtime gas impact.

Written by the indexing model from the issue text.