Graphics.Line: #7656-Line-rounded_rectangle BugFix

[podraco]

This merge request solves #7656. *improves the class to lock the maximum length between corners based on the minimum value between object length and width.

• adds the missing 4 control points
• made the drawing instruction a loop, that can be easily maintained
• changed the behavior of the segments parameter, this parameter now indicates the amount of segment that will be processed for each corner.
• the inner loop starts processing the top-right corner and goes clock backwards wise. But the radius_ parameters works the same. The array inside allows the normal standard behavior across kivy.

Be aware that this means the following *wh=min(width, height) : minumum value between height and width. *wh2 = (wh-1)//2 : half the minimum lenght.

New behavior for the segments parameter:

• if segment = 0 the canvas will draw a normal rectangle
• if segment >= 1: the canvas will draw a rounded rectangle with the number of segments per corner + the side flat lines.
• if segment > wh2, we use the wh2 value as maximum.

New radius behavior:

• all corner radius are checked to be less or equal to wh2
• all corners limit are wh2, this allows us to avoid some visual issues whenever the line has a specific kind of corner joint.
• all corners have a lower limit of 1 this help us to avoid adding a new logic block for radius_ = 0
• all corners are square. maybe not square corners might be added in the future (if i learn how to plot them).

Maintainer merge checklist

• [x] Title is descriptive/clear for inclusion in release notes.
• [x] Applied a Component: xxx label.
• [ ] Applied the api-deprecation or api-break label.
• [ ] Applied the release-highlight label to be highlighted in release notes.
• [ ] Added to the milestone version it was merged into.
• [ ] Unittests are included in PR.
• [x] Properly documented, including versionadded, versionchanged as needed.

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