Project Chooser: Slow to react when project changed if several documents need closing and opening

### What Happened?

Switching between two projects each with multiple documents open by clicking on their names in the drop-down list on the ChooseProject button did not produce any immediate action (and the dropdown remained open) leading the user to wonder whether the click had been registered. Presumable Code is busy closing/hiding the old project documents and opening/unhiding the new projects documents which can take >1 second.

### Steps to Reproduce

1. Open two projects
2. Open several documents in each
3. Switch between the two projects using the Choose Project button.

### Expected Behavior

There should be some visual feedback that the choice has been registered and is being implemented e.g. the dropdown should close and maybe a spinner shown in the active project widget until the new project is ready to use.

### OS Version

7.x (Horus)

### Software Version

Compiled from git

### Log Output

_No response_

### Hardware Info

_No response_

从 ChooseProject 按钮开始，在打开多个文档的情况下复现项目之间的切换，观察下拉菜单何时关闭以及新项目何时变得可用。未指定任何文件或测试；完成意味着提供即时的视觉反馈，例如关闭下拉菜单或在切换完成期间显示 spinner。

由索引模型根据 Issue 内容生成。