docs: Adds Use system dialogs Fiddle example

[yashints]

Description of Change

Refs #20442

Adds all the Use system dialogs:
✅ Open a file or directory
✅ Error dialog
✅ Information dialog
✅ Save dialog
examples from electron-api-demos into a runnable Fiddle example.

Checklist

• PR description included and stakeholders cc'd
• standard linter passes
• PR title follows semantic commit guidelines

Release Notes

Notes: Added the Use system dialogs example from electron-api-demos into a runnable Fiddle example.

[erickzhao]

For consistency's sake, could you break this down into 1 Fiddle per demo?

Also:

• Make links open in new browser window with shell.openExternal
• Remove obsolete CSS classes

[yashints]

Applied all of the above changes

[codebytere]

lgtm following changes

[release-clerk]

Release Notes Persisted

Added the Use system dialogs example from electron-api-demos into a runnable Fiddle example.