Improve ESM layout how-to guide

[MarcSkovMadsen]

The current ESM layout guide was migrated from ReactiveHTML guide. I think it could be improved by

• Changing the topic/ example to something more clearly layout like. For example as split.js layout.
• Adding handling for updating of children

Besides that I will

• fix some errors introduced in the reference guide since I wrote them.

Todo:

• Philipp: Make sure only one child (right) is updated when changed. Not both (right and left).
• Philipp: Remove ParamFutureWarning logged when using Child parameter.
• Philipp: Fix GridReact append and pop issue.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.22%. Comparing base (15a8241) to head (1ec9f20).
Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7088      +/-   ##
==========================================
- Coverage   82.22%   82.22%   -0.01%     
==========================================
  Files         328      328              
  Lines       49267    49269       +2     
==========================================
+ Hits        40509    40510       +1     
- Misses       8758     8759       +1     

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