feat: make it pop! (over) @W-18425406

[wjhsf]

Details

popover is a new global attribute, so we need to add it to our list of global attributes! Part of the popover feature are two new <button> attributes, popovertarget and popovertargetaction. The popovertarget attribute is an ID referencing another element, so it must be transformed in synthetic shadow mode for the attribute to work as expected.

Fixes #5340.

Does this pull request introduce a breaking change?

• 😮‍💨 No, it does not introduce a breaking change.
• 💔 Yes, it does introduce a breaking change.

Does this pull request introduce an observable change?

• 🤞 No, it does not introduce an observable change.
• 🔬 Yes, it does include an observable change.

GUS work item

[gaurav-rk9]

The spec mentions that these attributes can be applied to buttons. According to the button definition, "Some submittable elements can be, depending on their attributes, buttons. The prose below defines when an element is a button. Some buttons are specifically submit buttons." However, it is unclear to me where the specific prose defining buttons is located. Additionally, I noticed that these attributes are also mentioned in the input spec, suggesting that other elements might support these attributes as well.