feat(init/util): `tactic.trace`-like `trace_val` function
feat(init/util): `tactic.trace`-like `trace_val` function

Calling it `trace` and removing the old `trace` function does bad things with overloading

fpvandoorn/lean,Kha/lean,rlewis1988/lean,leanprover/lean,fpvandoorn/lean,digama0/lean,leanprover-community/lean,Kha/lean,leodemoura/lean,dselsam/lean,leanprover-community/lean,leodemoura/lean,digama0/lean,avigad/lean,leodemoura/lean,dselsam/lean,rlewis1988/lean,avigad/lean,fpvandoorn/lean,leodemoura/lean,avigad/lean,leanprover/lean,digama0/lean,fpvandoorn/lean,leanprover/lean,Kha/lean,fpvandoorn/lean,dselsam/lean,johoelzl/lean,leanprover-community/lean,avigad/lean,leanprover-community/lean,dselsam/lean,johoelzl/lean,fpvandoorn/lean,leanprover/lean,johoelzl/lean,Kha/lean,dselsam/lean,Kha/lean,johoelzl/lean,johoelzl/lean,digama0/lean,dselsam/lean,leanprover/lean,rlewis1988/lean,leodemoura/lean,leanprover-community/lean,rlewis1988/lean,digama0/lean,leodemoura/lean,digama0/lean,avigad/lean,avigad/lean,johoelzl/lean,leanprover/lean,leanprover-community/lean,rlewis1988/lean,Kha/lean,rlewis1988/lean