Check if autocomplete behaviour is still connected

While working on https://github.com/flutter/devtools/pull/6677

I noticed that we have autocomplete behaviour in the widget inspector search field.

I've never once seen it pop up though, so I wonder if maybe it got disconnected at some point.
If so we should discuss reconnecting it.
While discussing this we should discuss it's behaviour. If possible it would be nice if the user could use enter and shift+enter to navigate the search results. So we could tweak the autocomplete indexing while we are in the area.(See https://github.com/flutter/devtools/issues/6864)

https://github.com/flutter/devtools/blob/master/packages/devtools_app/lib/src/shared/ui/search.dart#L1253

从 packages/devtools_app/lib/src/shared/ui/search.dart 的第 1253 行附近开始，检查自动补全如何连接到 widget inspector 搜索字段。查看 issue 6864 和 pull request 6677 中的相关讨论；当当前行为已被理解，并且所需的自动补全以及使用 Enter/Shift+Enter 的导航行为已达成一致并实现时，工作就完成了。

由索引模型根据 Issue 内容生成。