Split project creation from add-to-project form

[eyeseast]

I think that this form belongs in its own modal:

• Creating a new project is a focused and intentional interaction that waits on a server response, so it creates a new UI context. This points to a modal being the correct space for this interaction.
• Creating a new project is a less common action when organizing documents. In this UI, we can assume the frequency of a user creating new projects is less than the frequency of picking existing projects.
• Use of a <details> element speaks to the current UI feeling too "cluttered" with the full creation form, but I think this misplaces the disclosure of additional interaction. Instead of hiding individual inputs from users, we should hide the entire form until the user makes an intentional interaction to create a new project.
• This project form has no opinion about the context it's rendered in, so it could appear in any kind of layout. This means we are not necessarily stacking modals inside one interface. Our current implementation of modals also supports layering, so the question is not "will this decision result in a nested modal?" but "is a modal the appropriate interaction in the context of this component?" In this case, the answer is yes. By reframing the question away from outcome and towards motivation, it allows us to think more critically about the use of a modal in the context of each component—the culmination of those decisions is a consisently behaved UI that's more coherent to users.

We also already have the EditProject component that defines this form, so I think reusing that instead of redefining it is the correct path here for ensuring consistency in creating projects going forward.

Originally posted by @allanlasser in #647 (comment)