feat(library/simplifier): add simplifier_monitor interface

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(library/simplifier): expose simplier and simplifier_monitor objects in the Lua API

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
test(tests/lean): add test using simplifier monitor for tracking failures

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