PERF: read_csv with memory_map=True when file encoding is UTF-8 (pandas-dev#43787)

Author: michal-gh

doc/source/whatsnew/v1.3.4.rst

@@ -32,14 +32,16 @@ Bug fixes
 - Fixed bug in :meth:`.GroupBy.mean` with datetimelike values including ``NaT`` values returning incorrect results (:issue:`43132`)
 - Fixed bug in :meth:`Series.aggregate` not passing the first ``args`` to the user supplied ``func`` in certain cases (:issue:`43357`)
 
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 .. _whatsnew_134.other:
 
 Other
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+- Improved performance of :meth:`pandas.read_csv` with ``memory_map=True`` when file encoding is UTF-8 (:issue:`43787`)
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