feat(shell/lean): support stdin redirection in server mode
feat(shell/lean): support stdin redirection in server mode

This is useful if you're debugging lean-server in an IDE which cannot
redirect stdin, and also if you want to run `gdb --args lean
--server=some.file`.

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