Fixing missed cases in mig_resub

[lee30sonia]

• There were some cases missing in the old mig_resub_functor (now called mig_enumerative_resub_functor to be distinguished from the other one calling resynthesis engines) due to the way how inverters were considered.
• The possibility of using constants as one of the fanins is also added and can be turned off by the flag use_constant.
• The checks of is_dead are removed in resubstitution and functional_reduction because this should be handled in foreach_gate.

[coveralls]

Pull Request Test Coverage Report for Build 464464960

• 2 of 86 (2.33%) changed or added relevant lines in 1 file are covered.
• 140 unchanged lines in 3 files lost coverage.
• Overall coverage decreased (-1.3%) to 80.179%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
include/mockturtle/algorithms/mig_resub.hpp	2	86	2.33%

Files with Coverage Reduction	New Missed Lines	%
include/mockturtle/algorithms/mig_resyn_engines.hpp	1	76.48%
include/mockturtle/algorithms/dsd_decomposition.hpp	3	87.5%
include/mockturtle/algorithms/mig_resub.hpp	136	22.6%

Totals
Change from base Build 454895153:	-1.3%
Covered Lines:	10857
Relevant Lines:	13541

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💛 - Coveralls