consider a more general option for defineCustomElement other than shadowRoot in incoming [email protected]

[lejunyang]

I noticed that Vue is going to add a shadowRoot option for defineCustomElement(37d2ce5)

I was wondering if we could use a more general option named as shadowOptions, which will be directly used for attachShadow like below:

this.attachShadow({ mode: 'open', ..._def.shadowOptions })

and if it's false or null, we won't call attachShadow anymore(same like shadowRoot=false)

There are a lot of options of attachShadow we are not able to customize for now.
Based on my experience, I believe closed shadowRoot and manual slotAssignment are seldom used but mandatory features. For component like watermark, I must use closed shadowRoot for safety reason(I have already implemented this component based on my customization, please refer to watermark component) And I wish that can be supported by official.

If Vue decides to support those options one by one in the future, there will be a lot of extra options