Implement Matplotlib format support and responsive Image sizing

[philippjfr]

• Adds support for Matplotlib.format parameter that allows rendering output to PNG and now also SVG
• Rewrites handling of sizing modes on Image types
• Fixes Images overlap plots in GridSpec #4268

[codecov]

Codecov Report

Merging #4514 (e08c6a5) into main (f0c64ae) will increase coverage by 0.18%.
The diff coverage is 98.29%.

@@            Coverage Diff             @@
##             main    #4514      +/-   ##
==========================================
+ Coverage   82.32%   82.50%   +0.18%     
==========================================
  Files         243      243              
  Lines       35579    35875     +296     
==========================================
+ Hits        29290    29599     +309     
+ Misses       6289     6276      -13     

Flag	Coverage Δ
ui-tests	36.12% <59.25%> (+0.24%)	⬆️
unitexamples-tests	74.23% <70.08%> (-0.02%)	⬇️

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Impacted Files	Coverage Δ
panel/pane/plot.py	69.16% <81.48%> (+2.22%)	⬆️
panel/pane/image.py	87.34% <97.22%> (+6.09%)	⬆️
panel/tests/pane/test_image.py	100.00% <100.00%> (ø)
panel/tests/pane/test_plot.py	100.00% <100.00%> (ø)
panel/tests/ui/pane/test_image.py	100.00% <100.00%> (ø)
panel/tests/util.py	90.00% <0.00%> (-1.82%)	⬇️
panel/util/__init__.py	87.60% <0.00%> (-0.43%)	⬇️
panel/io/state.py	70.39% <0.00%> (+0.34%)	⬆️

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