Motivation stemmed from PR in pandas in which I was trying to make searchsorted in pandas have a compatible signature with numpy without externalizing the sorter argument (it isn't used in the pandas implementation) by accepting a kwargs argument to swallow the sorter arg.

However, because np.searchsorted treats sorter like a positional argument in the internal call and NOT as a keyword argument as it should be based on the method signature, it was not possible to do so. This PR fixes that inconsistency as well as in all other np functions that use _wrapit in the implementation.

xref #12644 (pandas)