feat(library/elaborator): add support for proj/pair/sigma in the the higher-order unification procedure

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(frontends/lean/pp): bug in tuple/pair pretty printing

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
refactor(builtin/kernel): move the heq axioms into kernel.lean

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
refactor(builtin): remove dead module heq

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(util/lua): deadlock

Errors in the Lua library produce longjmps.
The longjmp will not unwind the C++ stack.
In the new test, the lock was not being released, and the system was deadlocking in the next call that tried to lock the environment

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>