Previously, we only supported very basic numbers and a single level of
text positioning support in the `x`, `y`, `dx` and `dy` attributes in
`<text>` and `<tspan>` SVG elements.
This improves our support for them in the following ways:
* Any `length-percentage` or `number` type value is accepted;
* Nested `<text>` and `<tspan>` use the 'current text position'
concept to determine where the next text run should go;
* We expose the attributes' values through the API.
Though we still do not support:
* Applying the `rotate` attribute;
* Applying transformations on a per-character basis.
* Proper horizontal and vertical glyph advancing (we just use the path
bounding box for now).
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.
More things need this than just the `<path>` element, so let's avoid
having to include `SVGPathElement.h` in places that don't need it.
Minor changes at the same time:
- Wrap it in a Path class
- Specify underlying type for PathInstructionType
- Make a couple of free functions into methods
- Give PathInstruction an operator==
No functionality changes.
