rustdoc-search: case-sensitive only when capitals are used

This is the "smartcase" behavior, described by vim and dtolnay.

tests/rustdoc-js/case.js

@@ -0,0 +1,17 @@
+const EXPECTED = [
+    {
+        'query': 'Foo',
+        'others': [
+            { 'path': 'case', 'name': 'Foo', 'desc': 'Docs for Foo' },
+            { 'path': 'case', 'name': 'foo', 'desc': 'Docs for foo' },
+        ],
+    },
+    {
+        'query': 'foo',
+        'others': [
+            // https://github.com/rust-lang/rust/issues/133017
+            { 'path': 'case', 'name': 'Foo', 'desc': 'Docs for Foo' },
+            { 'path': 'case', 'name': 'foo', 'desc': 'Docs for foo' },
+        ],
+    },
+];