Table rows render outside of the visible viewport when table reattaches to page

[mollykreis]

🐛 Bug Report

When the nimble-table reattaches to a page after being detached, the virtualizer and table scroll position are reloaded out of sync with each other. As a result, the table's rows don't render with the correct Y position in the table's viewport, causing either no rows to be visible or for there to be blank space between the header and the first rendered row. Interacting with the table's scrollbar fixes the problem.

💻 Repro or Code Sample

This issue was originally reported within SLE, so there are ways to get into this situation in an application. However, I was able to reproduce the problem within storybook by interacting with the DOM in dev tools.

1. Go to the nimble-table's storybook page with a large data set
2. Scroll down in the table (any amount)
3. In dev tools, assign the nimble-table element to a variable (say tableElement)
4. Using dev tools, delete the table from the DOM
5. Readd the table to the DOM (e.g. call appendChild(tableElement) on the nimble-theme-provider element in the storybook story)
6. Notice that the table rows don't render correctly. Depending on how much you scrolled down, either none or only some of the table's rows will render.

🤔 Expected Behavior

When the table is reattached, you should be able to see its rows.

😯 Current Behavior

When the table is reattached, its viewport is not filled with rows (though they do exist in the DOM).

💁 Possible Solution

The table and virtualizer's connectedCallback functions need to handle the case where the table is being reattached rather than attached for the first time. Specifically, this means that the virtualizer's rowContainerYOffset and the scroll position of the table's viewport need to be reloaded in a consistent state.

🔦 Context

In SLE, this is causing tables to load incorrectly after either hitting the "Back" button in the browser or when switching anchor-tab pages.

🌍 Your Environment

Does not appear to be browser/OS specific.