initAssetBaseURL: fall back to import.meta.url

While this will never work with old Edge it makes things easier during testing
where we can't set an id on the script tag. And we still don't know if supporting
old Edge is even needed.

packages/common/test/unit.js

@@ -37,8 +37,7 @@ suite('utils', () => {
 
     test('getAssetURL', () => {
         utils.initAssetBaseURL();
-        assert(utils.getAssetURL("foo/bar") === "foo/bar");
-        assert(utils.getAssetURL("foo/bar") === "foo/bar");
+        assert.equal(new URL(utils.getAssetURL("foo/bar")).pathname, "/foo/bar");
     });
 
     test('getThemeCSS', () => {

packages/common/utils.js

@@ -203,6 +203,10 @@ export const initAssetBaseURL = (id) => {
     if (document.currentScript && document.currentScript.src) {
         _assetBaseURL = document.currentScript.src;
     }
+
+    // XXX: Can't be parsed in (old) edge, but makes everything so much easier...
+    if (!_assetBaseURL)
+        _assetBaseURL = new URL('..', import.meta.url).href;
 };
 
 /**