fix(file): fix OLE-based file-type auto-detection (#3437)
**Summary**
A DOC, PPT, or XLS file sent to partition() as a file-like object is
misidentified as a MSG file and raises an exception in python-oxmsg
(which is used to process MSG files).
**Fix**
DOC, PPT, XLS, and MSG are all Microsoft OLE-based files, aka. Compound
File Binary Format (CFBF). These can be reliably distinguished by
inspecting magic bytes in certain locations. `libmagic` is unreliable at
this or doesn't try, reporting the generic `"application/x-ole-storage"`
which corresponds to the "container" CFBF format (vaguely like a
Microsoft Zip format) that all these document types are stored in.
Unconditionally use `filetype.guess_mime()` provided by the `filetype`
package that is part of the base unstructured install. Unlike
`libmagic`, this package reliably detects the distinguished MIME-type
(e.g. `"application/msword"`) for OLE file subtypes.
Fixes #3364
