doc search: fix mismatch between generator and renderer

This change revisits commit eb7fa6f066. I think the problem
is not in the rendering of index entries but on the generation
side. The generator was converting Xexprs to strings, except
that strings were left as-is, which is inconsistent. So,
I've reverted commit eb7fa6f066 and fixed the generator.

collects/scribblings/main/private/make-search.rkt

@@ -81,7 +81,7 @@
         [`() xexprs]
         [`("" . ,r) (compact r)]
         [`(,(? string? s) ...)
-         (list (apply string-append xexprs))]
+         (list (xexpr->string (apply string-append xexprs)))]
         [`(,(? string? s1) ,(? string? s2) . ,r)
          (compact `(,(string-append s1 s2) . ,r))]
         [`((span ([class ,c]) . ,b1) (span ([class ,c]) . ,b2) . ,r)

collects/scribblings/main/private/search.js

@@ -643,7 +643,7 @@ function UncompactUrl(url) {
 
 function UncompactHtml(x) {
   if (typeof x == "string") {
-    return SanitizeHTML(x);
+    return x;
   } else if (!(x instanceof Array)) {
     return alert("Internal error in PLT docs");
   } else if ((x.length == 2) && (typeof(x[0]) == "number")) {