Fix/save graphic for matplotlib

[prmukherj]

"save_graphic" for matplotlib windows was producing erroneous results. The behavior has been corrected now.

Sample usage:
From the example script generate two pyvista and two matplotlib plots and display them:

graphics = Graphics(session=solver_session)
mesh1 = graphics.Meshes["mesh-1"]
mesh1.show_edges = True
mesh1.surfaces_list = ["in1", "in2", "in3", "out1", "solid_up:1", "solid_up:1:830", "solid_up:1:830-shadow"]
mesh1.display("window-1")
mesh1.show_edges = False
mesh1.display("window-2")

and

plots_session_1 = Plots(solver_session)
xy_plot = plots_session_1.XYPlots["xy-plot"]
xy_plot.surfaces_list = ["outlet"]
xy_plot.y_axis_function = "temperature"
xy_plot.plot("window-9")
matplotlib_plots1 = Plots(solver_session)
residual = matplotlib_plots1.Monitors["residual"]
residual.monitor_set_name = "residual"
residual.plot("window-10")

Now try:
(for saving matplotlib figures):

from ansys.fluent.visualization.matplotlib import matplot_windows_manager
matplot_windows_manager.save_graphic(window_id="window-9",format="PNG")
matplot_windows_manager.save_graphic(window_id="window-10",format="PNG")

(for saving pyvista figures):

from ansys.fluent.visualization.pyvista import pyvista_windows_manager
pyvista_windows_manager.save_graphic(window_id="window-1",format="pdf")
pyvista_windows_manager.save_graphic(window_id="window-2",format="pdf")