Add the aegraph (acyclic e-graph) implementation crate. (#4909)

* Add the aegraph (acyclic egraph) implementation crate.

* fix crate-dep version for cranelift-entity (rebase error)

* Review feedback.

* Fix link in Markdown doc comment.

* Doc link fix again.

* add cranelift-egraph to publish list.

scripts/publish.rs

@@ -25,6 +25,7 @@ const CRATES_TO_PUBLISH: &[&str] = &[
     "cranelift-codegen-shared",
     "cranelift-codegen-meta",
     "cranelift-codegen",
+    "cranelift-egraph",
     "cranelift-reader",
     "cranelift-serde",
     "cranelift-module",