Use TextEdit instead of QQC2.TextArea in SelectableLabel, add context menu to SelectableLabel

SelectableLabel wont resize properly when using QQC2.TextArea, likely due to TextArea having it's own resizing and background handling.

TextEdit is handled more like a Label is, so it resizes correctly. We just have to manually make it use the proper colors, which was doable with Kirigami.

SelectableLabel also has its own, smaller context menu now.

BUG:493581

Using following code snippet:

    Kirigami.PromptDialog {
        id: textPromptDialog
        title: "Title"
        subtitle: "empty"
        Component.onCompleted: {
            subtitle = "A long subtitle which should change the width of the PromptDialog <a href='https://google.com'>googel</a>"
        }
    }

Before	After