fldf3: electron-builder: Set linux.executableName, not linux.desktop.Exec

Per error message in CI when trying to do it the desktop.Exec way

fix-Linux-desktop-file-tag1: electron-builder: Add '--no-sandbox' launch arg for Linux build targets

Fixes Dev Tools not being able to be opened, among other subtle issue.

This is a frequently reported bug, and we try to apply this workaround
elsewhere, it's just that the .desktop file that electron-builder
generates skips the workaround we have applie e.g. in the /us/bin/pulsar
launcher script.