HANK: add a routine to check the steady-state input

matlab/+hank/check_steady_state_input.m

matlab/+hank/private/check_consistency.m

matlab/+hank/private/check_fun.m

matlab/+hank/private/check_isfield.m

matlab/+hank/private/check_isstruct.m

matlab/+hank/private/check_missingredundant.m

matlab/+hank/private/check_permutation.m

meson.build

tests/hank/expect_error.m

tests/hank/ks.mod

tests/hank/ks_ar1_ss.m

tests/hank/ks_iid_ss.m

tests/hank/ks_ss.mat