Border has a 1 pixel thickness even when it's thickness property is set to 0 - fix

[kubaflo]

Issues Fixed

Fixes #20156

Before	After

[pjcollins]

Fix seems reasonable to me and appears to fix the issue, though I'll defer to @jsuarezruiz for a final review.

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[dustin-wojciechowski]

Tested to work on IOS, Android, and Windows:
(Windows pictured below)

[mattleibow]

Thanks for this PR, I feel this issue has been around for some time and was annoying, but now we have fixes.!

I just have a Q on the relationship between a few lines, but I am also hoping to take advantage of your PR and the nice person you are to maybe add some more tests for other permutations of the border, stroke, shape and thickness so that we don't have to write hundreds of UI tests but still protect our future selves from breaking this.

[kubaflo]

Hi, @mattleibow you're right I've added a commit with your suggested changes :)
When it comes to this part

if (StrokeShape is Shape strokeShape && StrokeThickness == 0)
{
    strokeShape.StrokeThickness = StrokeThickness;
}

I don't know why this condition is needed StrokeThickness == 0. Everything is okay without it, but I might not have tested it enough. Maybe @jsuarezruiz who introduced this line in this PR https://github.com/dotnet/maui/pull/14403/files might tell us more :)

[mattleibow]

Waiting on screenshots from CI...

[mattleibow]

/azp run

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