Treat other items as functions for the purpose of type-based search

constants and statics are nullary functions, and struct fields are unary functions.

functions (along with methods and trait methods) are prioritized over other
items, like fields and constants.

tests/rustdoc-js-std/const-is-nullary-func.js

@@ -0,0 +1,7 @@
+const EXPECTED = {
+    'query': '-> char',
+    'others': [
+        { 'path': 'std::char', 'name': 'from_digit' },
+        { 'path': 'std::char', 'name': 'MAX' },
+    ],
+}