renamed str::view -> slice_DBG_BRWD
renamed str::slice -> slice_DBG_UNIQ
changed vec slice method -> to_owned()
renamed vec view method  -> slice_V_DBG_BRWD
removed str::slice_DBG_UNIQ
back-renamed slice_DBG_BRWD, slice_V_DBG_BRWD -> slice, slice_DBG_UNIQ -> slice_unique
auto merge of #5466 : Kimundi/rust/view-slice-rename, r=bstrie

A slice now always refers to something that returns an borrowed pointer, views don't exist anymore. If you want to have an explictit copy of a slice, use `to_owned()`