Add ability to send macOS-specific modifier keys (Command, Option) to boot_command

[hisaac]

Description

I'm using Packer to spin up macOS VMs with Tart's Packer plugin. It works great, but one quality of life improvement I'd love to see is the ability to use correct references to macOS-specific modifier keys (Command and Option keys) in the boot_command.

Specifically, what I'd like to have is:

1. The ability to use <leftCmdOn> and its left/right off/on variants to send the Command key.
2. The ability to use <leftOptOn> and its left/right off/on variants to send the Option key.

Right now, <leftAlt> an <rightAlt> both map to left and right Command respectively, so I assume these could just be aliased somehow.

I haven't figured out how to send an Option key command yet though, so I'm not sure how that would be implemented.

I'm willing to do this work myself if someone could first give me some guidance or ideas on where and how this modification might be made.

[hisaac]

I'm not sure at what layer these changes would need to be made, so I've also opened a matching issue on the cirruslabs/packer-plugin-tart repo: cirruslabs/packer-plugin-tart#174

[hisaac]

I see there was some discussion and maybe some work related to this done in the main packer repository a while ago.

• boot_command syntax for sending custom key codes packer#5634
• Add <leftCmdOn>, <leftCmdOff> keys for macOS guests packer#5633
• add super key (vmware builder) packer#5681

Perhaps that work can be duplicated here somehow?

@mcandre, it seems like you were the primary person interested in this in the main packer repository. Any thoughts or ideas on how similar functionality could be brought to the plugin sdk?