Button missing getErrorsAsString() fixes #8084 Debug: Not calling undefined method anymore. If the form contained a submit button the call would fail and the debug of the form wasn't possible. Now it will work in all cases. This fixes #8084

Adding a test for the fix of getErrorAsString on Form.
Was throwing a fatal because of a method that did not exist on
the new element type button.
merged branch mikeSimonson/patch-1 (PR #8247)

This PR was submitted for the master branch but it was merged into the 2.3 branch instead (closes #8247).

Discussion
----------

[Form][BUG]Button missing getErrorsAsString() fixes #8084

Debug: Not calling undefined method anymore.
If the form contained a submit button the call would fail and the debug of the form wasn't possible.
Now it will work in all cases.
This fixes #8084

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #8084
| License       | MIT

Commits
-------

dab0688 [Form][BUG]Button missing getErrorsAsString() fixes #8084 Debug: Not calling undefined method anymore. If the form contained a submit button the call would fail and the debug of the form wasn't possible. Now it will work in all cases. This fixes #8084