Removing global document references (#1482)

fix for options `recordCanvas: true`: 
* replace document.createElement with doc.createElement in rrweb-snapshot code
* Eoghan: add a regression test to prevent future accidental use of `document` instead of `doc`.  This test can be excised if a new feature can only be run in the browser and not in the jsdom environment

.changeset/proud-clocks-hope.md

@@ -0,0 +1,5 @@
+---
+"rrweb-snapshot": patch
+---
+
+(when `recordCanvas: true`): ensure we use doc.createElement instead of document.createElement to allow use in non-browser e.g. jsdom environments