Add output variables to better control base output

[sebnitu]

Problem

There's currently no control over what gets output when @vrembem/base is included in a project.

Solution

To better control the base output, this PR introduces the $output and $output-[module] variables that take a boolean value and will either enable or disable a modules CSS output. Setting $output will be passed to all other module output variables as their default option. This allows you to disable all modules and add only the ones you need vs having them all output by default and disable the ones you don't need.

Examples

// Will disable the output of the type module
@use "@vrembem/base" with (
  $output-type: false
);

// Will disable all modules, but enables the base module
@use "@vrembem/base" with (
  $output: false,
  $output-base: true
);

Additional changes

This PR also does the following:

• Moves spacing into the base component
• Adds $spacing and $spacing-map vars to core
• Both base and utility components pass core spacing variables as their defaults for equivalent variables
• Adds scroll-box() mixin