Form component - use forms anywhere

[pxpm]

WHY

BEFORE - What was wrong? What was happening before this PR?

It was almost impossible to use the backpack forms anywhere else other than the create operation.

O opened the PR to get early feedback from @tabacitu

AFTER - What is happening after this PR?

This PR adds two new components. FormComponent e FormModalComponent.

The first one display the form whenever the component is added on page, eg:

The second one, the modal, brings a button that open the form in a modal, and uses ajax for handling:

Is it a breaking change?

Theoretically no.

How can we test the before & after?

??

If the PR has changes in multiple repos please provide the command to checkout all branches, eg.:

git checkout "dev-branch-name" &&
cd vendor/backpack/crud && git checkout crud-branch-name &&
cd ../pro && git checkout pro-branch-name &&
cd ../../..

[pxpm]

superseeder by #5809