Use fuzzy-matching to improve cache hit rates with PostScriptEvaluator

This improves performance, without any noticeable regressions when running `gulp browsertest --noChrome` locally on Windows.
Testing the new `pr5134` test-case locally in the viewer:
 - With the `master` branch and `isEvalSupported = true`, page 2 renders in approx. 350 milliseconds.
 - With the `master` branch and `isEvalSupported = false`, page 2 renders in approx. 1550 milliseconds.
 - With this patch, which forces `isEvalSupported = false`, page 2 renders in approx. 990 milliseconds.

Hence this isn't obviously enough to close the performance gap, but it *may* still be helpful.

src/core/function.js

@@ -456,7 +456,10 @@ class PDFFunction {
       for (i = 0; i < numInputs; i++) {
         value = src[srcOffset + i];
         input[i] = value;
-        key += value + "_";
+        // Fuzzy-match to increase the cache hit rate which helps improve
+        // performance, at the expense of absolute rendering quality.
+        // (At least in the test-suite the differences are imperceivable).
+        key += Math.round(value * 1e8) / 1e8 + "_";
       }
 
       const cachedValue = cache[key];

src/display/api.js

@@ -279,7 +279,7 @@ function getDocument(src) {
     Number.isInteger(src.maxImageSize) && src.maxImageSize > -1
       ? src.maxImageSize
       : -1;
-  const isEvalSupported = src.isEvalSupported !== false;
+  const isEvalSupported = false; // src.isEvalSupported !== false;
   const isOffscreenCanvasSupported =
     typeof src.isOffscreenCanvasSupported === "boolean"
       ? src.isOffscreenCanvasSupported

test/pdfs/pr5134.pdf.link

@@ -0,0 +1 @@
+https://web.archive.org/web/20140211020222/http://www.coachusa.com/CoachUsaAssets/files/97/route45.pdf

test/test_manifest.json

@@ -2221,6 +2221,15 @@
     "lastPage": 1,
     "type": "eq"
   },
+  {
+    "id": "pr5134",
+    "file": "pdfs/pr5134.pdf",
+    "md5": "6a701a163472e071a2519348b55cbac1",
+    "rounds": 1,
+    "link": true,
+    "firstPage": 2,
+    "type": "eq"
+  },
   {
     "id": "issue5599",
     "file": "pdfs/issue5599.pdf",