Reland "Redesign Straight-Line Strength Reduction (SLSR) (#162930)" (#169614)

This PR implements parts of
https://github.com/llvm/llvm-project/issues/162376

- **Broader equivalence than constant index deltas**:
- Add Base-delta and Stride-delta matching for Add and GEP forms using
ScalarEvolution deltas.
- Reuse enabled for both constant and variable deltas when an available
IR value dominates the user.
- **Dominance-aware dictionary instead of linear scans**:
  - Tuple-keyed candidate dictionary grouped by basic block.
- Walk the immediate-dominator chain to find the nearest dominating
basis quickly and deterministically.
- **Simple cost model and best-rewrite selection**:
- Score candidate expressions and rewrites; select the highest-profit
rewrite per instruction.
- Skip rewriting when expressions are already foldable or
high-efficiency.
- **Path compression for better ILP**:
- Compress chains of rewrites to a deeper dominating basis when a
constant delta exists along the path, reducing dependent bumps on
critical paths.
- **Dependency-aware rewrite ordering**:
- Build a dependency graph (basis, stride, variable delta producers) and
rewrite in topological order.
- This dependency graph will be needed by the next PR that adds partial
strength reduction.
- **Correctness enhencment**
- Fix a correctness issue that reusing instructions with the same SCEV
may introduce poison.

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Co-authored-by: Kazu Hirata <kazu@google.com>