Add optional DividerItemDecoration parameters in Browser TabsTray

[gabrielluong]

In the [Tabs Tray Design], we need to be able to add a divider in between each items in the RecyclerView. We can achieve this by adding a DividerItemDecoration in BrowserTabsTray.

┆Issue is synchronized with this Jira Task

[gabrielluong]

Closing as WONTFIX. We don't need to expose the ItemDecoration bit of the BrowserTabsTray's RecyclerView, because BrowserTabsTray is a RecyclerView. You can simply add the decoration on to the view itself.

val tray = BrowserTabsTray(context, attrs)
tray.addItemDecoration(object : RecyclerView.ItemDecoration() {
    override fun getItemOffsets(
        outRect: Rect,
        view: View,
        parent: RecyclerView,
        state: RecyclerView.State
    ) {
        // Do things here.
    }
})