Release desktop builds for direct download with an installer and self-updater

Our goal is to have Graphite update just as easily as apps like Chrome, Firefox, VS Code, and Discord.

### Windows

For `.msi` installers, we should probably use the open source installer generator, [Inno Setup](https://jrsoftware.org/isinfo.php), which is also notably used by VS Code and Git for Windows. And then probably roll our own auto-updater, which might use Inno Setup to install updates with the [`/SILENT`](https://jrsoftware.org/ishelp/index.php?topic=setupcmdline) flag. Some background research [here](https://www.reddit.com/r/csharp/comments/1oyxjkq/is_my_inno_setup_selfupgrade_check_logic/) and [here](https://stackoverflow.com/questions/53073973/how-to-automatically-update-an-application-installed-with-inno-setup). We can reference the 2.5k lines of Rust code in [Inno Updater](https://github.com/microsoft/inno-updater) written by Microsoft for updating VS Code. There is also this recent and very detailed [explanation](https://github.com/microsoft/vscode/issues/249239) about the flow and recent robustness improvements Microsoft made to it.

### Mac

TODO: Investigate how to create a `.dmg` installer, including custom background graphics to make the drag-into-Applications-folder process clear. We will probably need to roll our own auto-updater for this platform as well, hopefully with some code reuse. But [Squirrel](https://github.com/Squirrel/Squirrel.Mac), used by Electorn and VS Code, or [Sparkle](https://sparkle-project.org/), could be other options if they aren't complex to integrate in our Rust codebase and give enough flexibility so we can do our own update checks and UI. Investigation will be required to figure out how to self-update the contents of an app package.

### Linux

TODO: Distribute the [ELF](https://en.wikipedia.org/wiki/Executable_and_Linkable_Format) file and dependencies in a `.zip`? Is there any other sort of self-unpacking installer besides a ZIP we can use instead? Can we roll an auto-updater for this too? This would be in addition to distribution through common package managers: #584.