Fix GridLayoutManager Layout calculation

[myroot]

Description of Change

Replaced widthConstraint/heightConstraint to explicit width/height, if explicit width/height was valid.

GridlayoutManager returns the explicit width/height as a measure result if it was valid

maui/src/Core/src/Layouts/GridLayoutManager.cs

Line 289 in 3ae0029

var height = _explicitGridHeight > -1 ? _explicitGridHeight : GridHeight();

maui/src/Core/src/Layouts/GridLayoutManager.cs

Line 306 in 3ae0029

var width = _explicitGridWidth > -1 ? _explicitGridWidth : GridWidth();

But, Layout calculation was not affected by explicit width/height. so, ArrangeChildren is not working propertly
It was fixed

Issues Fixed

Fixes #7681

[rmarinho]

/azp run

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[jsuarezruiz]

/azp run

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