From the SVG spec
The value of the ‘viewBox’ attribute is a list of four numbers <min-x>,
<min-y>, <width> and <height>, separated by whitespace and/or a comma...
Currently try_parse_view_box will fail to parse the attribute if the
values are separated by commas.
This change replaces try_parse_view_box with a more correct
implementation. It will reside in the AttributeParser.cpp. This new
implementation correctly handles comma-separated viewBox values, and is
also more robust against invalid inputs.
Additionally, it adds a new test case to ensure viewBox values with
various syntax are parsed correctly and invalid values are rejected.
Special handling for SVGClipPathElement and SVGMaskElement, which use a
a ViewBox and PreserveAspectRatio value internally, has been moved to
`SVGFormattingContext`.
