Make project import interactive

Right now, importing Java projects is happening at startup. I am aware that there is the "interactive" mode, but all that allows me to do is to veto the import of the projects. (If I select "later", how do I later import the projects? There seems to be no "Import Projects" command 🤷 )

Let's consider making the import more interactive by

• allow the user to pick which directories will be imported
• allow the user to select which import will import a directory is two or more want to import a given directory
• allow importers to ask the user to fix problems while importing (think "no compatible Java version" could be fixed by selecting a JDK directory).

In order to implement something like this, we'd have to move control of the import process to the vscode-java side instead of handling import in the language server. That would also alllow us to give more precise feedback if something goes wrong with the import. IMO.

首先跟踪启动时的导入流程、现有的交互模式，以及 VS Code 扩展与语言服务器之间的边界。明确用户如何选择目录和导入器、解决导入器问题，并在之后触发导入；当这些交互能够提供精确反馈，而不依赖仅在启动时进行的导入时，即表示完成。