gh-119342: Fix a potential denial of service in plistlib (GH-119343)

gh-119342: Fix a potential denial of service in plistlib (GH-119343)

Reading a specially prepared small Plist file could cause OOM because file's
read(n) preallocates a bytes object for reading the specified amount of
data. Now plistlib reads large data by chunks, therefore the upper limit of
consumed memory is proportional to the size of the input file.