Accept stdin input for fe CLI

### What is wrong?

`solc` has an option to pass input from stdin:
```bash
echo 'pragma solidity ^0.8.8; contract Example { function sub(int32 a, int32 b) public pure returns (int32) { return a - b; } }' | solc -
```
which seems quite handy for debugging and quick checking stuff.

An idea of passing `-` as first argument and then piping stdin into the command seems familiar to Solidity developers, so we can adopt such thing too.

### How can it be fixed

If `input_file == "-"`, read stdin and process it instead of input file.

Start at the fe CLI entry point and trace where input_file is parsed and read. Test the command with '-' as the first argument and piped Solidity input; done means stdin is processed instead of an input file.

Written by the indexing model from the issue text.