[BUG] a bug specific to the combination of match_aspect=True and "stretch" sizing modes

[user4015990]

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ALL software version info (bokeh, python, notebook, OS, browser, any other relevant packages)

bokeh=2.1.1
python=3.8.3
OS=windows 10
brower=Firefox 79

Description of expected behavior and the observed behavior

Expect to keep the aspect ratio of image as is when the browser window is resized.
However, the aspect ratio of image will change when the browser window is resized.

Complete, minimal, self-contained example code that reproduces the issue

# code goes here between backticks
from bokeh.plotting import figure, show
from bokeh.layouts import layout
p = figure(match_aspect=True)
p.image_url(['https://static.bokeh.org/logos/logo.png'],0,0,1,1)
layer = layout(p, sizing_mode='stretch_both')
show(layer)

Stack traceback and/or browser JavaScript console output

Screenshots or screencasts of the bug in action