Add client-side options support

# Problem
If there are static options passed into the element, the options are deleted on request for filtered options.

# Request
Client-side options should be supported and have filtering available. TBD: Do we allow both client-side (such as default options) *and* server-side options?

# Implementation concerns
## Accessibility
Ensure that any default / client-side options are announced when the input is focused. `screen-reader-announcements.ts` can assist with this.

When the options list isn't visible, an `aria-describedby` should be added to the input pointing to the feedback element. This should only be if the element has client-side options. Remove this `aria-describedby` when the user interacts with any key, and add it back in when the auto-complete-element is blurred. cc @github/accessibility and @jscholes for reference. "aria-live won't cut it" for this scenario

## Developer Notes
There is some initial setup done in `autocomplete.ts` to detect client-side options, but all of this can be removed / reworked, as long as accessibility considerations are met.

从 autocomplete.ts 开始，检查现有的客户端选项检测，然后阅读 screen-reader-announcements.ts 了解无障碍行为。跟踪在经过筛选的请求期间如何移除选项，并定义客户端选项与服务端选项之间受支持的交互。完成的标准是客户端选项仍然可用、筛选功能正常，并且涵盖所描述的焦点、键盘、blur 和 aria-describedby 行为。

由索引模型根据 Issue 内容生成。