add subset of electron dialog methods

[sethvincent]

This adds the following dialog methods to the ipc/api:

• electron.dialog.showOpenDialog()
• electron.dialog.showSaveDialog()
• electron.dialog.showMessageBox()
• electron.dialog.showErrorBox()

The main use case I have is showOpenDialog/showSaveDialog to avoid needing File System APIs and be able to easily do some localdrive->mirror-drive->hyperdrive stuff based on user input.

Otherwise it's File System API -> stream from ui to pear-end -> stream to somewhere -> ...

Unless there's another option I'm missing!

I skipped the sync methods and showCertificateTrustDialog as they seem a lot less likely to be used but could add them.

I didn't get super far because I got confused about the build process. Followed the npm pack instructions but after install never saw the methods show up. I'm clearly doing something wrong 😅

Anyway, I can make changes, add docs, etc. if this is something you're looking to add.

[geordangesink]

@sethvincent gui/ipc.js is part of preload, same as api.js... api.js is the ui api exposed to the "frontend" when importing in an app, while gui/ipc.js is the ipc that connects from preload to main... so you need a handler in gui/gui.js (main process) and call the electron methods there.