Add border styles for top and left in VisualCell

[ravetroll]

The cell formatting is incomplete for the top border and left border of the cell. This change implements the styling that is missing

[anmcgrath]

Hey ravetroll thanks for the PR. The SetFormatCommand already handles setting adjacent cell borders for left/top borders, although I suppose it doesn't work for cells in the first row/column. We should consider only rendering the actual top/left borders for the first visual cell in either axis.

[ravetroll]

`
public static void OutlineCell(SheetCell _selection, string color, int width)
{

_selection.Format = new CellFormat()
{

    BorderBottom = new Border()
    {
        Color = color,
        Width = width
    },
    BorderTop = new Border()
    {
        Color = color,
        Width = width
    },
    BorderLeft = new Border()
    {
        Color = color,
        Width = width
    },
    BorderRight = new Border()
    {
        Color = color,
        Width = width
    }

};

}
`

When I run this code i use for drawing borders around a single cell, only the bottom and right border is drawn.

[ravetroll]

I am looking into what can be done to put borders inside the region, rather than put borders on the adjacent cell

[ravetroll]

Ok I made a little test app BlazorApp1, and I made some changes to SetFormatCommand on top of the VisualCell styling changes I made previously. I wanted to make the surrounding cells format the line on the inside of the cells in the selected range and I have achieved that. I have broken some of test tests regarding formatting but at least you can see a working example of how I think the border formatting for surroundings should work.