feat(ui5-table): add growing on scroll

[ilhan007]

Background
Adds "loadMore" capability to the Table upon user scroll (previously possible trough "More" button - see the PR #2589). With this feature, the "load-more" event will be fired when the user scrolls to the table's end.

FIXES: #2570

BREAKING_CHANGES:

• hasMore removed, use growing instead
• loadMoreText has been renamed to moreText
• loadMoreSubtext has been renamed to moreSubtext

API Changes

• added growing from type TableGrowingType with 3 options:
  -- "None" - growing is off (default)
  -- "Scroll" - Table's load-more is fired upon user scrolls to the table's end
  -- "Button" - Table's load-more is fired upon pressing a "More" button
• added busy - when set the table's opacity is reduced and busy indicator shown
• removed hasMore (in favour of growing)
• loadMoreText renamed to moreText
• loadMoreSubtext renamed to moreSubtext

Usage

• set growing to "Scroll" to make the table tracks the user scrolling (not supported in IE)
• set growing to "Button" to get the special "More" button(row) at the table's bottom
• set busy to show/hide busy indicator over the table.
• set moreText if you need custom text within the "More" button
• set moreSubtext if you need additional description within the "More" button
• listen to the load-more event to load more rows, when the user presses the additional row

Example

<ui5-table id="myTable" growing="Button" more-text="Load more" more-subtext="4 of 10"></ui5-table>
<ui5-table id="myTable" growing="Scroll"></ui5-table>

myTable.addEventListener("load-more", function() {

   // show busy indicator
    myTable.busy = true; 
    
    // load new entries
    rowsToLoad.forEach(() => {
	tbl.appendChild(document.createElement('ui5-table-row'));
    );
    
    // hide busy indicator
     myTable.busy = false; 
});

Busy Indicator placement

• For modern browsers we make use of position: sticky to how the busy indicator always in the center of the Table while user scrolls.
• For IE, we use position: absolute (as sticky is not supported), which will show the busy indicator in the center, but when the table becomes longer, the busy indicator will be scrolled out.

[vladitasev]

I like the API (having an enum instead of 2 booleans)!
We could probably discuss the names and we can merge