rustdoc: use Set for ignored crates, instead of string matching

Author: notriddle

src/librustdoc/html/static/js/main.js

@@ -533,9 +533,11 @@ function preLoadCss(cssUrl) {
         // ignored are included in the attribute `data-ignore-extern-crates`.
         const script = document
             .querySelector("script[data-ignore-extern-crates]");
-        const ignoreExternCrates = script ? script.getAttribute("data-ignore-extern-crates") : "";
+        const ignoreExternCrates = new Set(
+            (script ? script.getAttribute("data-ignore-extern-crates") : "").split(",")
+        );
         for (const lib of libs) {
-            if (lib === window.currentCrate || ignoreExternCrates.indexOf(lib) !== -1) {
+            if (lib === window.currentCrate || ignoreExternCrates.has(lib)) {
                 continue;
             }
             const structs = imp[lib];