Fix source plugin's undefined index issues, schema issues and unnecessary trailing whitespaces and empty lines

1. +++ b/migrations/d7_webform.yml
   @@ -18,7 +18,8 @@ process:
   +  # TODO submit label should be migrated as part of the "elements".
   +  # 'settings/form_submit_label': submit_text
   

   Is this a @todo for this issue or for a separate issue?

2. +++ b/src/Plugin/migrate/source/d7/D7Webform.php
   @@ -288,7 +288,10 @@ class D7Webform extends DrupalSqlBase implements ImportAwareInterface, RollbackA
   +      // Description can be missing.
   

   By "can be missing", do you mean "is optional"?

Even with this applied, I'm still getting:

Notice: Undefined index: size in Drupal\webform_migrate\Plugin\migrate\source\d7\D7Webform->buildFormElements() (line 346 of modules/webform_migrate/src/Plugin/migrate/source/d7/D7Webform.php).

Notice: Undefined index: type in Drupal\webform_migrate\Plugin\migrate\source\d7\D7Webform->buildFormElements() (line 381 of modules/webform_migrate/src/Plugin/migrate/source/d7/D7Webform.php).

Now I'm still seeing:

Notice: Undefined index: type in Drupal\webform_migrate\Plugin\migrate\source\d7\D7Webform->buildFormElements() (line 384 of …/modules/webform_migrate/src/Plugin/migrate/source/d7/D7Webform.php)

384 line is if ($extra['type'] == 'textfield') {

@Wim Leers, can you check the value of extra column in webform_component table for the component that throws this notice?

I'm looking at webform/components/number.inc (D7 version) and it expects ['extra']['type'] always to be available (there are no additional checks).

Considering that data is corrupted for some reason, I think we can fallback to textfield type, but let's try to figure out why it's empty 🤔

Hi mates
Thank you very much for working on this direction.
I'd be very appreciate for having some info in issue description.

It's very complicate to find out issue goal only by issue name,

As I see this issue is blocker for adding tests.
Patch #10 already allowing to run tests added in #3172139: Enable project testing, and add a kernel test and a source database and files fixture
Gonna commit it.

I just found one more:
Notice: Undefined offset: 1 in /var/www/docroot/modules/contrib/webform_migrate/src/Plugin/migrate/source/d7/D7Webform->buildItemsString() line 978

Can be reproduced in the following case:
D7 component type: grid
questions value: "1|Hello...\n"

Given the string ends with \n, the result of $items = explode("\n", $rawString); in getItemsArray() is:

[
'1|Hello...',
'',
];

Adding a quick fix to trim the string before exploding.

Yep, that would be better 😊

Created merge request with patch webform_migrate-undefined_index-3172154-18_0.patch from #18.