perf: ensure Expr.replaceExpr preserve DAG structure in Exprs

[leodemoura]

No description provided.

[leodemoura]

!bench

[leanprover-community-mathlib4-bot]

Mathlib CI status (docs):

• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 4eb842560ce2c8f3b99a2f2867e87585e9159ecf --onto ba3565f441a4533490c339ead6d9ee5b1220110b. (2024-07-18 02:26:35)

[leanprover-bot]

Here are the benchmark results for commit d198a7a.
There were significant changes against commit 4eb8425:

  Benchmark     Metric                  Change
  ========================================================
+ reduceMatch   instructions             -5.3% (-1829.0 σ)
+ stdlib        attribute application    -2.6%   (-30.5 σ)
+ stdlib        fix level params         -2.5%   (-38.5 σ)
+ stdlib        tactic execution         -1.5%  (-151.3 σ)