Organize Imports should be smarter about single-letter types

When there's an unresolved single-letter type usage in the code, doing Organize Imports should not blindly import a type it finds

Environment

• Operating System: Windows 10
• JDK version: 14
• Visual Studio Code version: 1.45.0
• Java extension version: 0.61.0

Steps To Reproduce

1. do Organize Imports on the code below, while there's a single type T available for import (in my case it was inside Apache POI, but you could just create a trivial T.java file

import java.util.Map;

//import org.apache.poi.ss.formula.functions.T;

public class Bar {

    public void print(Comparable<T> bar, Map<Integer, T> whatever) {

    }

}

Current Result

the type T is imported

Expected Result

the actual issue here is that I forgot to specify the type variable T. Ideally, the extension would give a single error saying exactly that. If that's not feasible, it should at least ask confirmation before importing single-letter types, even if there's only a single one available: the chances that the user actually wants to import such a type are much smaller than the chance that there's an error w.r.t. type variables

从 Organize Imports 的入口点开始，使用此 issue 中的 Java 代码片段复现该行为，并使用一个可供导入的单字母类型（例如 T）。当扩展不再盲目导入这个单字母类型，而是报告缺少类型变量的问题或请求确认时，这项工作就完成了。