Applicable only on auto-layout frames. Determines whether the primary axis has a fixed length (determined by the user) or an automatic length (determined by the layout engine).
primaryAxisSizingMode: "FIXED" | "AUTO"
Auto-layout frames have a primary axis, which is the axis that resizes when you add new items into the frame. For example, frames with "VERTICAL"
layoutMode resize in the y-axis.
"FIXED": The primary axis length is determined by the user or plugins, unless the
layoutAlignis set to “STRETCH” or
"AUTO": The primary axis length is determined by the size of the children. If set, the auto-layout frame will automatically resize along the counter axis to fit its children.