Generate selection as a group or frame

[gavinmcfarland]

To make it easier to plug-and-play generated code it would be useful if there was an option to generate the selected nodes to a frame or a group. Plugin creators could then export the group or frame from a JS module and either use as is or ungroup. The generator would create a placeholder frame and replace figma.currentPage with the placeholder frame. Or in the case of a group, collect all top-level nodes and add them to a group.

Frames

const placeholder = figma.createFrame()
// ...
placeholder.appendChild(frame_1_15)
// ...
placeholder.appendChild(frame_1_16)

Groups

const placeholder = figma.group([frame_1_15, frame_1_16], figma.currentPage)

Potentially in addition to this, we might want to introduce an ungroupNode() helper.