[PM] Show the pass argument in pre/post-pass IR dumps

This patch adds each pass' pass argument in the header for IR dumps.
For example:

Before:

```
    *** IR Dump Before InstructionSelect ***
```

After:

```
    *** IR Dump Before InstructionSelect (instruction-select) ***
```

The goal is to make it easier to know what argument to pass to
command line options like `debug-only` or `run-pass` to further
investigate a given pass.