Improve spacing and alignment of menus

[emilk]

What

Based on:

• CSS-like shadows with offset, spread, and blur emilk/egui#4232
• Add some distance between parent menu and submenu emilk/egui#4230
• Better align menus with the button that opened them emilk/egui#4233

Before

After

Checklist

• I have read and agree to Contributor Guide and the Code of Conduct
• I've included a screenshot or gif (if applicable)
• I have tested the web demo (if applicable):
  • Using newly built examples: app.rerun.io
  • Using examples from latest main build: app.rerun.io
  • Using full set of examples from nightly build: app.rerun.io
• The PR title and labels are set such as to maximize their usefulness for the next release's CHANGELOG
• If applicable, add a new check to the release checklist!

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[Wumpf]

[Wumpf]

kinda strange they still use paper money in Futurama, never actually noticed before