Apply pre-processors to ESM children

[philippjfr]

An oversight in the way ESM components implemented rendering of children meant that preprocessors weren't applied. This meant functionality such as HoloViews linking and the application of design modifiers didn't happen in some scenarios.

[codecov]

Codecov Report

Attention: Patch coverage is 91.66667% with 3 lines in your changes missing coverage. Please review.

Project coverage is 87.10%. Comparing base (b6ae1ed) to head (3bc5b12).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
panel/custom.py	91.66%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #7799       +/-   ##
===========================================
+ Coverage   71.35%   87.10%   +15.74%     
===========================================
  Files         345      346        +1     
  Lines       52945    52970       +25     
===========================================
+ Hits        37781    46137     +8356     
+ Misses      15164     6833     -8331     

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