rustdoc-search: allow :: and ::

This restriction made sense back when spaces separated function
parameters, but now that they separate path components, there's
no real ambiguity any more.

Additionally, the Rust language allows it.

tests/rustdoc-js-std/parser-errors.js

@@ -143,6 +143,15 @@ const PARSED = [
         userQuery: "a::::b",
         error: "Unexpected `::::`",
     },
+    {
+        query: "a:: ::b",
+        elems: [],
+        foundElems: 0,
+        original: "a:: ::b",
+        returned: [],
+        userQuery: "a:: ::b",
+        error: "Unexpected `:: ::`",
+    },
     {
         query: "a::b::",
         elems: [],
@@ -314,24 +323,6 @@ const PARSED = [
         userQuery: 'a<->',
         error: 'Unexpected `-` after `<`',
     },
-    {
-        query: "a:: a",
-        elems: [],
-        foundElems: 0,
-        original: 'a:: a',
-        returned: [],
-        userQuery: 'a:: a',
-        error: 'Unexpected `:: `',
-    },
-    {
-        query: "a ::a",
-        elems: [],
-        foundElems: 0,
-        original: 'a ::a',
-        returned: [],
-        userQuery: 'a ::a',
-        error: 'Unexpected ` ::`',
-    },
     {
         query: "a<a>:",
         elems: [],

tests/rustdoc-js-std/parser-paths.js

@@ -15,6 +15,54 @@ const PARSED = [
         userQuery: "a::b",
         error: null,
     },
+    {
+        query: "a:: a",
+        elems: [{
+            name: "a:: a",
+            fullPath: ["a", "a"],
+            pathWithoutLast: ["a"],
+            pathLast: "a",
+            generics: [],
+            typeFilter: -1,
+        }],
+        foundElems: 1,
+        original: 'a:: a',
+        returned: [],
+        userQuery: 'a:: a',
+        error: null,
+    },
+    {
+        query: "a ::a",
+        elems: [{
+            name: "a ::a",
+            fullPath: ["a", "a"],
+            pathWithoutLast: ["a"],
+            pathLast: "a",
+            generics: [],
+            typeFilter: -1,
+        }],
+        foundElems: 1,
+        original: 'a ::a',
+        returned: [],
+        userQuery: 'a ::a',
+        error: null,
+    },
+    {
+        query: "a  ::  a",
+        elems: [{
+            name: "a  ::  a",
+            fullPath: ["a", "a"],
+            pathWithoutLast: ["a"],
+            pathLast: "a",
+            generics: [],
+            typeFilter: -1,
+        }],
+        foundElems: 1,
+        original: 'a  ::  a',
+        returned: [],
+        userQuery: 'a  ::  a',
+        error: null,
+    },
     {
         query: 'A::B,C',
         elems: [