Provide tools to analyze the files in a database.

Recently, I tried to use CodeQL to analyze my project, and all the steps succeeded without any warnings. However, after running some queries I realized that it was missing most of the files.

As a user, it would be nice to be able to list the files that are included in the database with just a command.

After talking with @adityasharad , he suggested using a simple query that just lists all the files:

```
/**
* @description "List all the files"
* @id debug.listfiles
* @kind problem
* @name list-files
* @tags maintanability
* @problem.severity recommendation
**/
import cpp

from File f
select f, "This file is in the repo"
```

It would be nice to have something like that built into the application.

CodeQL CLI と issue に示されている単純な `debug.listfiles` クエリから始め、その出力をデータベースに含まれているファイルと比較します。これらのファイルを一覧表示する組み込みコマンドを定義し、現在分析から除外されているファイルが表示されることを確認します。

索引モデルが issue の本文から書いたものです。