quiver/quiver3: Overhaul input processing, validation, and add BISTs. * scripts/plot/draw/private/__quiver__.m: Overhaul numeric input validation. Simplify input classification using numeric input count switch statements and avoid quiver3 miscount due to scale factor. Add error messages for all valid numeric input combinations including vector x,y,z and scale factor. Move newplot command from quiver/quiver3 into __quiver__ after numeric input validation. Add hax as an output argument to return any changes back to calling function. * scripts/plot/draw/quiver.m: Remove newplot call. Update __quiver__ call to include hax as a return variable. Update docstring with note that line style and name-value pairs can both be provided but linstyle must appear first. Add BISTs to check standard inputs with single and multiple arrows, arrowhead shape, vector and array inputs, proper treatment of scaling factor "off", some simple input styles, and input validation BISTs to cover all numeric input errors. Added known failing BIST for linestyle+pair arrowhead showing when it should stay off (bug #64143). * scripts/plot/draw/quiver3.m: Remove newplot call. Update __quiver__ call to include hax as a return variable. Update docstring with note that line style and name-value pairs can both be provided but linstyle must appear first. Add BISTs to check standard inputs with single and multiple arrows, vector and array inputs, and input validation BISTs to cover all numeric input errors. * etc/NEWS.9.md: Update quiver/quiver3 improvement description under General Improvements.

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