[SVG2] Allow leading and trailing whitespace in svg attributes

LayoutTests/svg/animations/script-tests/svglength-animation-invalid-value-2.js

 description("Test SVGLength animation with invalid value: No spaces before value.");
 createSVGTestCase();
 
 // Setup test document
 var rect = createSVGElement("rect");
 rect.setAttribute("id", "rect");
 rect.setAttribute("x", "0");
 rect.setAttribute("width", "100");
 rect.setAttribute("height", "100");
 rect.setAttribute("fill", "green");
 rect.setAttribute("onclick", "executeTest()");
 
 var animate = createSVGElement("animate");
 animate.setAttribute("id", "animation");
 animate.setAttribute("attributeName", "width");
 animate.setAttribute("begin", "click");
 animate.setAttribute("dur", "4s");
-animate.setAttribute("from", "   100px");
-animate.setAttribute("to", "   200px");
+animate.setAttribute("from", "   100pxERROR");
+animate.setAttribute("to", "   200pxERROR");
 rect.appendChild(animate);
 rootSVGElement.appendChild(rect);
 
 // Setup animation test
 function sample1() {
     // Check initial/end conditions
     shouldBeCloseEnough("rect.width.animVal.value", "100");
     shouldBe("rect.width.baseVal.value", "100");
 }
 
 function sample2() {
     shouldBeCloseEnough("rect.width.animVal.value", "0");
     shouldBe("rect.width.baseVal.value", "100");
 }
 
 function executeTest() {
     const expectedValues = [
         // [animationId, time, sampleCallback]
         ["animation", 0.0,   sample1],
         ["animation", 2.0,   sample2],
         ["animation", 3.999, sample2],
         ["animation", 4.001, sample1]
     ];
 
     runAnimationTest(expectedValues);
 }
 
 var successfullyParsed = true;