chore(test): prepare tests to be run with Puppeteer-Firefox (#3833)

This patch aligns Puppeteer testing infrastructure with the approach
we use in Puppeteer-Firefox.

This patch:
- makes all tests accept Puppeteer object as a function argument
  rather than require it statically. This way we can pass either
  Puppeteer or Puppeteer-Firefox to drive tests.
- renames the `puppeteer.spec.js` into `launcher.spec.js`. The
  `puppeteer.spec.js` is now the entry point for all cross-browsers
  tests.

test/golden-chromium/csscoverage-involved.txt

@@ -0,0 +1,16 @@
+[
+  {
+    "url": "http://localhost:<PORT>/csscoverage/involved.html",
+    "ranges": [
+      {
+        "start": 149,
+        "end": 297
+      },
+      {
+        "start": 327,
+        "end": 433
+      }
+    ],
+    "text": "\n@charset \"utf-8\";\n@namespace svg url(http://www.w3.org/2000/svg);\n@font-face {\n  font-family: \"Example Font\";\n  src: url(\"./Dosis-Regular.ttf\");\n}\n\n#fluffy {\n  border: 1px solid black;\n  z-index: 1;\n  /* -webkit-disabled-property: rgb(1, 2, 3) */\n  -lol-cats: \"dogs\" /* non-existing property */\n}\n\n@media (min-width: 1px) {\n  span {\n    -webkit-border-radius: 10px;\n    font-family: \"Example Font\";\n    animation: 1s identifier;\n  }\n}\n"
+  }
+]