Refactor: change "Add Form" button link and styles

[glaubersilva]

Resolves GIVE-999

Description

This PR makes the "Add Form" button from the form list view create a new form using the visual form builder. It also updates the styles to keep the consistency with the WordPress secondary and primary buttons.

Affects

The "Add Form" button from the form list view.

Visuals

https://www.loom.com/share/caff9f3671eb4defab5b470e391ae55e?sid=e9fee7e0-7817-4af9-ae05-1d9228918d74

Testing Instructions

1. Go to Give > All Forms and make sure the new styles are applied to the buttons;
2. Go to User > Profile and change the admin color scheme;
3. Check if the new color schema got applied to the buttons;
4. Click on the "Add Form" button and make sure it's creating new forms using the Visual Form Builder.

Pre-review Checklist

• Acceptance criteria satisfied and marked in related issue
• Relevant @unreleased tags included in DocBlocks
• Includes unit tests
• Reviewed by the designer (if follows a design)
• Self Review of code and UX completed

[jdghinson]

All good!

[pauloiankoski]

@jdghinson Currently, the buttons are being styled slightly different from WP native buttons (32px vs 30px height and 500 vs 400 font-weight). Was that intentional?

Native on top, modified on bottom

[jdghinson]

@pauloiankoski Yes, the native looks smaller.

[glaubersilva]

@pauloiankoski This is ready for re-review.

[pauloiankoski]

👍🏻

[rickalday]

Passed manual QA tests.