[Parquet][Python] Inconsistent default values for Parquet `pre_buffer`

[pitrou]

Describe the bug, including details regarding any error messages, version, and platform.

Some Parquet reading APIs in PyArrow have pre_buffer default to False and others to True.

The default value should probably be made consistent. On the C++ side, the default value is true.

Component(s)

Python, Parquet

[pitrou]

@AlenkaF @rok