Use of the compute_decision_rules function to factorize code (Ref.#1773)

Regarding issue Ref. #1173 (closed) 73, use the compute_decision_rules function instead of the resol function in the following files: 'dsge_simulated_theoretical_conditional_variance_decomposition.m' (line 145), 'dsge_simulated_theoretical_correlation.m' (line 118), 'dsge_simulated_theoretical_covariance.m' (line 116), 'dsge_simulated_theoretical_variance_decomposition.m' (line 144), 'identification_analysis.m' (line 136), 'osr1.m' (line 146), 'osr_obj.m' (line 50), 'reversed_extended_path.m' (line 51), 'selec_posterior_draws.m' (line 145), 'simulated_moment_uncertainty.m' (line 74), 'stoch_simul.m' (line 109).