Use arrow function with various Array methods

A lot of this is quite old code, which we can shorten slightly by using arrow functions instead of "regular" functions.

src/core/chunked_stream.js

@@ -414,9 +414,7 @@ class ChunkedStreamManager {
       }
     }
 
-    chunksToRequest.sort(function (a, b) {
-      return a - b;
-    });
+    chunksToRequest.sort((a, b) => a - b);
     return this._requestChunks(chunksToRequest);
   }
 

src/core/fonts.js

@@ -576,9 +576,7 @@ function getRanges(glyphs, toUnicodeExtraMap, numGlyphs) {
   if (codes.length === 0) {
     codes.push({ fontCharCode: 0, glyphId: 0 });
   }
-  codes.sort(function fontGetRangesSort(a, b) {
-    return a.fontCharCode - b.fontCharCode;
-  });
+  codes.sort((a, b) => a.fontCharCode - b.fontCharCode);
 
   // Split the sorted codes into ranges.
   const ranges = [];
@@ -1777,9 +1775,7 @@ class Font {
       }
 
       // removing duplicate entries
-      mappings.sort(function (a, b) {
-        return a.charCode - b.charCode;
-      });
+      mappings.sort((a, b) => a.charCode - b.charCode);
       const finalMappings = [],
         seenCharCodes = new Set();
       for (const map of mappings) {

src/core/jbig2.js

@@ -374,9 +374,7 @@ function decodeBitmap(
   // Sorting is non-standard, and it is not required. But sorting increases
   // the number of template bits that can be reused from the previous
   // contextLabel in the main loop.
-  template.sort(function (a, b) {
-    return a.y - b.y || a.x - b.x;
-  });
+  template.sort((a, b) => a.y - b.y || a.x - b.x);
 
   const templateLength = template.length;
   const templateX = new Int8Array(templateLength);

src/core/xml_parser.js

@@ -321,11 +321,7 @@ class SimpleDOMNode {
     if (!this.childNodes) {
       return this.nodeValue || "";
     }
-    return this.childNodes
-      .map(function (child) {
-        return child.textContent;
-      })
-      .join("");
+    return this.childNodes.map(child => child.textContent).join("");
   }
 
   get children() {