Electron Releases

The previous squirrel.mac patch cleaned up all staged update directories before starting a new download. This kept disk usage bounded, but it broke quitAndInstall() if called while a subsequent checkForUpdates() was in flight — the already-staged bundle would be deleted out from under it.

This reworks the patch to:

• Read ShipItState.plist and preserve the directory it references
• Delete only truly orphaned update.XXXXXXX directories
• Refactor the enumerate-and-delete logic into a shared helper so the existing pruneUpdateDirectories still does a full wipe on launch

Disk footprint stays bounded (at most 2 dirs: staged + in-progress) and quitAndInstall() remains safe to call mid-check.

Fixes #50200

Test plan

• e test --runners=main -g "autoUpdater behavior" passes on macOS
• Updated should preserve the staged update directory and prune orphaned ones when a new update is downloaded — asserts 1 dir during first download, 2 dirs during second (staged preserved + new), and that the original staged dir is among them
• New update-race fixture — calls quitAndInstall() while a second checkForUpdates() is downloading; the staged install should succeed
• New update-triple-stack fixture — 3 sequential update downloads without restart; directory count never exceeds 2

Notes: Fixed an issue on macOS where calling autoUpdater.quitAndInstall() could fail if checkForUpdates() was called again after an update was already downloaded.