[0.1.9] Add non-interactive mode

[jessarcher]

This PR introduces a non-interactive mode for Prompts.

When Prompts are non-interactive, they will attempt to return the configured default value instead of prompting. Most prompts have a safe default when none is provided. An exception will be thrown if the default value does not pass any validation checks.

This is useful when prompts occur in a non-interactive environment, such as a scheduled task, queued job, CI, or deploy script.

The behaviour is currently mixed, depending on the scenario. #63 prevented prompts from waiting indefinitely for input when the fallback was not triggered, but everything now depends on the fallback to handle non-interactive mode. When using a Symfony fallback, there are some inconsistencies. For example, the choice component doesn't allow you to select nothing in interactive mode but will return null in non-interactive mode. With this PR, the fallbacks no longer need to be used for non-interactive mode - just for Windows and when testing (for now).

This is a breaking change because Laravel depends on the fallback when running tests and the non-interactive mode will take over in a CI testing environment. If we release this change in v0.2, Laravel can update its version constraint and ensure interactive mode is enabled when testing. The companion PR is at laravel/framework#48468 Edit: We can release this as 0.1.9 and update the minimum version in the framework. This will avoid conflicts for users that have other packages that currently depend on ^0.1.

In the future, I would like to prevent the need for fallbacks when testing so that fallback mode is only required for Windows environments (and maybe that can even be solved with #17).

This also paves the way for #57, which needs to know when Laravel commands are explicitly told to be non-interactive (via the -n argument), regardless of the presence of a tty.

Fixes #64