[Proposal] Visualize dependency graph.

### Problem
I have a large number of build commands and packages that depend on each other and I would like to visually inspect these relationships to help with debugging and documentation.

### Proposed solution
I would love a command like "wireit --visual" that would show you the graph for the specific command being run, and if no command is being run for the whole project. This could be setup to work both between separate packages and between different commands

```mermaid
graph TD;
common:build-->core:build;
common:build-->common:css;
feature1:build-->common:build;
feature2:build-->common:build;
feature2:build-->feature1:build
feature1:test-->feature1:build
```

The above shows the sort of information I would want to know. The name of the package and the name of the build script. Here is very simple POC that uses the wireit Analyzer and creates a visualization with mermaidjs. It might also make sense to make this part of the vs-code extension instead of an option in the CLI

https://github.com/deebloo/wireit-visualizer