Replace OrderedDict with dict

[cdeil]

Modernise code base a bit by replacing OrderedDict with dict.
Should be complementary and not touch the lines from #6632 I hope.

[codecov]

Codecov Report

Attention: Patch coverage is 84.78261% with 7 lines in your changes are missing coverage. Please review.

Project coverage is 82.88%. Comparing base (385617b) to head (1fbd0a8).
Report is 5 commits behind head on main.

Files	Patch %	Lines
panel/layout/grid.py	57.14%	3 Missing ⚠️
panel/io/notebook.py	0.00%	1 Missing ⚠️
panel/io/resources.py	0.00%	1 Missing ⚠️
panel/io/server.py	0.00%	1 Missing ⚠️
panel/layout/gridstack.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6637   +/-   ##
=======================================
  Coverage   82.88%   82.88%           
=======================================
  Files         313      313           
  Lines       46132    46119   -13     
=======================================
- Hits        38236    38228    -8     
+ Misses       7896     7891    -5     

Flag	Coverage Δ
ui-tests	39.98% <17.39%> (-0.02%)	⬇️
unitexamples-tests	71.18% <84.78%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.