Bug report

A memory leak occurs during every frame draw when PySide2 is used with Python3. This issue was already fixed for PySide in the method matplotlib.backends.backend_qt5agg.FigureCanvasQtAgg.paintEvent
However, an additional check for QT_API == 'PySide2' is needed.

Code for reproduction

import matplotlib
matplotlib.use('Qt5Agg')
import matplotlib.pyplot as plt
plt.plot([1,2],[1,2])
plt.show()

Actual outcome

When a redraw of the figurecanvas is forced, the program memory increases steadily. For example during resizing the popup window.

Expected outcome

Constant memory during ui execution.

Matplotlib version

• Operating system: Windows 10
• Matplotlib version: 2.2.2
• Matplotlib backend (print(matplotlib.get_backend())): Qt5Agg
• Python version: 3.7

all packages are pip installed