Replace Riot with Element in docs and comments

This only covers the simple cases of references to issues and repos. More
complex areas, such as deployment scripts, will be handled separately.

Part of https://github.com/vector-im/element-web/issues/14864

src/theme.js

@@ -202,7 +202,7 @@ export async function setTheme(theme) {
     return new Promise((resolve) => {
         const switchTheme = function() {
             // we re-enable our theme here just in case we raced with another
-            // theme set request as per https://github.com/vector-im/riot-web/issues/5601.
+            // theme set request as per https://github.com/vector-im/element-web/issues/5601.
             // We could alternatively lock or similar to stop the race, but
             // this is probably good enough for now.
             styleElements[stylesheetName].disabled = false;