feat: add default cli flag

[nohehf]

This PR adds the --default=<default_pattern> flag to glob CLI.
It allows one to pass a default pattern that will be used if no positional argument is given.
This is especially useful when glob is aliased to some command. For instance, we can have in a package.json:

{
  [...],
  "scripts": {
    "test": "glob -c \"<test_command>\" --default \"./**/*.(spec|test).ts\""
    }
}

This allows one to pass a glob to select tests or run all tests if nothing is passed.
I currently use glob to pass files to our test command, hence the PR, but it likely has many other potential applications.
I intended to write a test, but looking at the codebase, I'm unsure if there is a way to test glob when used in CLI mode (via src/bin.ts). Please let me know if I'm wrong.

[isaacs]

Oh it looks like I forgot to check in the bin test. I'll fix that today.

Seems like --default would be a useful addition. 👍

[nohehf]

Hey @isaacs any updates on this ? Thx!

[nohehf]

Ty @isaacs :)