perf(donation-forms): create a helper function to get the default level id.

[emgk]

User Story

As a Developer, I want a helper function which returns the default level id and amount as well by donation form id so that I don't have to loop through each of the price levels to get the default level id and it's amount.

Also it will reduce the repitetion of code:
https://github.com/search?q=org%3AWordImpress+isset%28+%24price%5B%27_give_default%27%5D+%29+%26%26+%24price%5B%27_give_default%27%5D+%3D%3D%3D+%27default%27&type=Code

Current Behavior

Currently to get the default level id of the donation form I have to loop through each time to get the default level id of the donation form.

Expected Behavior

I expect to have a helper function which returns default level id by donation form id.

Possible Solution

Create a helper function with param { $form_id } to get the the default level id.

Tasks

• Create a helper function to get the default level id.