Increase the delta of the "weight" field to support reordering more than 20 blocks in a section

Why don't we count the number of elements we are weighting, to prevent this from ever being an issue in the future? \Drupal\workflows\Form\WorkflowEditForm::form has an example of this:

    $state_weight_delta = round(count($states) / 2);
...
        'weight' => [
          '#type' => 'weight',
          '#title' => t('Weight for @title', ['@title' => $state->label()]),
          '#title_display' => 'invisible',
          '#default_value' => $state->weight(),
          '#attributes' => ['class' => ['state-weight']],
          '#delta' => $state_weight_delta,
        ],

Would also be good to test this.

Patch for drupal 9.

Verified and tested by applying the patch #7.On adding more than 20 blocks in the section , counts accordingly gets increased in the row weights section.It looks good to me.Can be moved to RTBC.RTBC +1.

Steps to test -
1. Go to admin site.
2. Go to /admin/modules.
3. Enable the layout builder and discovery.
4. Go to admin/structure/block/block-content
5. Add custom block.
6. Go to admin/structure/types/manage/article/display/default/layout.
7. In the section , add 34 blocks.Re order it.
8. Click on edit icon in the block , click on move.
9. On the right side , pop-up gets opened , you will see the row weights.
10. Row weights should be according to the blocks added in the section.If block is 34 than -17 to 17 will display in row weights.

Before -

After -

The fix looks good, but this needs automated test coverage

Closed #3208972: Layout Builder MoveBlockForm weight field limited to 20 items. as duplicate.

Here's a fail test. It's pretty simple, but a couple notes...

1. I add 25 blocks to a new section at one point in the test. The test fails on any number over 20.
2. After adding 25 identical blocks, I cannot rely on assertRegionBlocksOrder because that function expects unique blocks.

Test failed as expected. Removing tag.

Here's the patch from #7 applied atop the fail patch.

Note that the interdiff includes changes related to running all test now while only running the updated test in #16. Saving energy, time, money, etc.

Triggering for 10.1

This issue is being reviewed by the kind folks in Slack, #needs-review-queue-initiative. We are working to keep the size of Needs Review queue [2700+ issues] to around 400 (1 month or less), following Review a patch or merge request as a guide.

Change passes 10.1
Issue summary has no more remaining tasks and clear proposed solution.

Fail patch proves this issue.

Committed/pushed to 10.1.x, cherry-picked to 10.0.x and 9.5.x, thanks!