feat(library/simplifier): contextual simplifications

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(library/simplifier): improve contextual simplifications

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
test(tests/lean): add test disabling contextual simplifications

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(library/simplifier): improve contextual simplifications

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
test(tests/lean): add test for congruence theorem that uses an argument before simplification

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
test(tests/lean): add test for congruence theorem that uses an argument before simplification