Implement text rise for the SVG back-end

The property and the setter for text rise were already present, but they
were never used or called. This patch completes the implementation by
calling the setter when the operator is encountered and by using the
text rise value when rendering text.

src/display/svg.js

@@ -562,6 +562,9 @@ SVGGraphics = (function SVGGraphicsClosure() {
             this.setTextMatrix(args[0], args[1], args[2],
                                args[3], args[4], args[5]);
             break;
+          case OPS.setTextRise:
+            this.setTextRise(args[0]);
+            break;
           case OPS.setLineWidth:
             this.setLineWidth(args[0]);
             break;
@@ -782,9 +785,16 @@ SVGGraphics = (function SVGGraphicsClosure() {
         current.tspan.setAttributeNS(null, 'fill', current.fillColor);
       }
 
+      // Include the text rise in the matrix since the `pm` function creates
+      // the SVG element's `translate` entry. Work on a copy to not alter the
+      // original text matrix.
+      let matrix = current.textMatrix.slice();
+      if (current.textRise !== 0) {
+        matrix[5] += current.textRise;
+      }
+
       current.txtElement.setAttributeNS(null, 'transform',
-                                        pm(current.textMatrix) +
-                                        ' scale(1, -1)');
+                                        pm(matrix) + ' scale(1, -1)');
       current.txtElement.setAttributeNS(XML_NS, 'xml:space', 'preserve');
       current.txtElement.appendChild(current.tspan);
       current.txtgrp.appendChild(current.txtElement);