fix: left frozen section shoudn't go over viewport width, fix #473

[ghiscoding]

• fixes Expanding frozen columns outside the viewport makes scrolling impossible #473
• with frozeen grid, we have 2 horizontal scrolling and if any of the column width on the left section goes over the viewport total width then we completely lose the scrolling on the right section (as described in issue Expanding frozen columns outside the viewport makes scrolling impossible #473)
• also note that the PR adds a new grid option frozenRightViewportMinWidth which is set to 100 by default and could be customized to a different minimum width for the right section of a frozen grid

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