Show loading message for b-table.

There is already a show-empty message when a b-table is empty. However, when a b-table is still being loaded, this message appears, which causes confusion.

I suggest to implement show-loading attr for b-table.

Thanks!

[tmorehouse]

@ghenry PR #2196 added in a new slot for table-busy. Whenever the table is in the busy state, and the named slot exists, then the content of that slot will be show instead of an empty table or previously rendered rows.

[tmorehouse]

You could place your table followed by a spinner component inside a div element as such:

<div class="table-container">
  <b-table busy.sync="isBusy" ... >
  </b-table>
  <my-spinner v-if="isBusy" class="table-spinner" />
</div>

and use a CSS sibling selector to position the spinner when busy

.table-container: {
  position: relative;
  width: 100%;
}
.b-table[aria-busy="true"] + .table-spinner {
  /* this assumes that the spinner component has a width and height */
  position: absolute;
  left: 50%
  top: 50%;
  transform: translate(-50%, -50%);
  z-index: 10; /* make sure spinner is over table */
}