Simplify PButton styling

[aaazzam]

Part of a series of PRs to simplify styling for PButton.

This series of PRs is trying to do two things:

• reduce the surface area of our design tokens for better maintenance. Right now we have things like --p-color-default-button-bg that is a pointer to 'transparent' and is used in exactly one place.
• make adding or changing button variants easier. I'd like to make a more uniform interface to our components around sizes (we have small: bool or size: string inconsistently), but our specific styling of PButton and other components makes it incredibly hard to change variants since they create a polynomial number of orthogonal BEM classes to maintain.

wish me luck!

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[pleek91]

right now we have things like --p-color-default-button-bg that is a pointer to 'transparent' and is used in exactly one place.

Yeah I don't think we need all these aliases. If we're using a design token we should use it directly rather making it look like its another token but its actually just an alias.

I'd like to make a more uniform interface to our components around sizes (we have small: bool or size: string inconsistently),

Yessss, idk how we ended up here but I'd love these to be consistent.