DOC: replace np.ma functions' return types with `MaskedArray` (#18964)
DOC: replace np.ma functions' return types with `MaskedArray` (#18964)

Relevant issue: #16751

Co-authored-by: paxcodes <5850fdfacfd98aa23175abccc24401a5d3b33157@users.noreply.github.com>
Co-authored-by: IrinaMaria <d847ef2750aaaeaa3c495cc589d3c5a59e5d5d11@users.noreply.github.com>
jakirkham/numpy,numpy/numpy,pdebuyl/numpy,jakirkham/numpy,endolith/numpy,seberg/numpy,rgommers/numpy,endolith/numpy,charris/numpy,seberg/numpy,pdebuyl/numpy,charris/numpy,endolith/numpy,charris/numpy,seberg/numpy,jakirkham/numpy,simongibbons/numpy,rgommers/numpy,simongibbons/numpy,jakirkham/numpy,anntzer/numpy,anntzer/numpy,mattip/numpy,numpy/numpy,mhvk/numpy,mhvk/numpy,mhvk/numpy,mhvk/numpy,anntzer/numpy,numpy/numpy,rgommers/numpy,jakirkham/numpy,numpy/numpy,simongibbons/numpy,mattip/numpy,pdebuyl/numpy,mattip/numpy,rgommers/numpy,mhvk/numpy,pdebuyl/numpy,seberg/numpy,simongibbons/numpy,endolith/numpy,charris/numpy,mattip/numpy,simongibbons/numpy,anntzer/numpy