rustdoc: add support for type filters in arguments and generics

This makes sense, since the search index has the information in it,
and it's more useful for function signature searches since a
function signature search's item type is, by definition, some type
of function (there's more than one, but not very many).

tests/rustdoc-js/generics-impl.js

@@ -5,6 +5,8 @@ const QUERY = [
     'Aaaaaaa -> bool',
     'Aaaaaaa -> usize',
     'Read -> u64',
+    'trait:Read -> u64',
+    'struct:Read -> u64',
     'bool -> u64',
     'Ddddddd -> u64',
     '-> Ddddddd'
@@ -36,6 +38,17 @@ const EXPECTED = [
             { 'path': 'generics_impl::Ddddddd', 'name': 'ggggggg' },
         ],
     },
+    {
+        // trait:Read -> u64
+        'others': [
+            { 'path': 'generics_impl::Ddddddd', 'name': 'eeeeeee' },
+            { 'path': 'generics_impl::Ddddddd', 'name': 'ggggggg' },
+        ],
+    },
+    {
+        // struct:Read -> u64
+        'others': [],
+    },
     {
         // bool -> u64
         'others': [

tests/rustdoc-js/generics.js

@@ -2,6 +2,8 @@
 
 const QUERY = [
     'R<P>',
+    'R<struct:P>',
+    'R<enum:P>',
     '"P"',
     'P',
     'ExtraCreditStructMulti<ExtraCreditInnerMulti, ExtraCreditInnerMulti>',
@@ -20,6 +22,20 @@ const EXPECTED = [
             { 'path': 'generics', 'name': 'alpha' },
         ],
     },
+    {
+        // R<struct:P>
+        'returned': [
+            { 'path': 'generics', 'name': 'alef' },
+        ],
+        'in_args': [
+            { 'path': 'generics', 'name': 'alpha' },
+        ],
+    },
+    {
+        // R<enum:P>
+        'returned': [],
+        'in_args': [],
+    },
     {
         // "P"
         'others': [

tests/rustdoc-js/primitive.js

@@ -3,6 +3,8 @@
 const QUERY = [
     "i32",
     "str",
+    "primitive:str",
+    "struct:str",
     "TotoIsSomewhere",
 ];
 
@@ -17,6 +19,14 @@ const EXPECTED = [
             { 'path': 'primitive', 'name': 'foo' },
         ],
     },
+    {
+        'returned': [
+            { 'path': 'primitive', 'name': 'foo' },
+        ],
+    },
+    {
+        'returned': [],
+    },
     {
         'others': [],
         'in_args': [],