support -depend on code generation

Hi,

Today, we need to do 2 calls for generation the code and get the generated files:

```
antlrTool G.g4 -o dir
```

```
antlrTool -depend G.g4
```

It would be nice if those two features can be executed in one single call, like:

```
antlrTool G.g4 -depend -o dir
```

Thanks

The issue names no files or tests. Start by locating the command-line argument handling for -depend and the code-generation path; make a single invocation support both dependency output and generated files, then verify the combined antlrTool G.g4 -depend -o dir command.

Written by the indexing model from the issue text.