added cell and row context flyouts

[w-ahmad]

Closses #38

Description

This PR enhances the TableView by adding support for displaying context flyouts for rows and cells.

New Properties

• RowContextFlyout Set's context flyout for TableView rows.
• CellContextFlyout Set's context flyout for TablevIew cells.

New Events

• RowContextFlyoutOpening fired before showing context flyout.
• CellContextFlyoutOpening fired before showing context flyout.

New types

• TableViewRowContextFlyoutEventArgs

public partial class TableViewRowContextFlyoutEventArgs : HandledEventArgs
{
    public TableViewRowContextFlyoutEventArgs(int index, TableViewRow row, object item, FlyoutBase flyout)
    {
        Index = index;
        Row = row;
        Item = item;
        Flyout = flyout;
    }

    public int Index { get; }
    public TableViewRow Row { get; }
    public object Item { get; }
    public FlyoutBase Flyout { get; }
}

• TableViewCellContextFlyoutEventArgs

public partial class TableViewCellContextFlyoutEventArgs : HandledEventArgs
{
    public TableViewCellContextFlyoutEventArgs(TableViewCellSlot slot, TableViewCell cell, object item, FlyoutBase flyout)
    {
        Slot = slot;
        Cell = cell;
        Item = item;
        Flyout = flyout;
    }

    public TableViewCellSlot Slot { get; }
    public TableViewCell Cell { get; }
    public object Item { get; }
    public FlyoutBase Flyout { get; }
}