Dialog title and button label

[joezappie]

Two fields that I think are useful that Electron's dialogs implement, but this spec doesn't is:

• Ability to change the dialogs title
• Ability to change the button label instead of just generic save/open.

window.showSaveFilePicker({
        title: 'Download Diagnostic Log',
        buttonLabel: 'Save Log',
});

I think being able to specify these leads to better usability as it can remind the user of what action they are currently doing.