refactor(extra): move extra to builtin

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
chore(builtin): cleanup cmake file

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
refactor(library/basic_thms): move the proof of all basic theorems to a .Lean file

This commit also adds several new theorems that are useful for implementing the simplifier.
TODO: perhaps we should remove the declarations at basic_thms.h?

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
refactor(library/basic_thms): move the proof of all basic theorems to a .Lean file