Newline character in HtmlTag causes unwanted whitespace

Addressed #90

- reverted changes to #81 (interdiff against it)
- added deprecation (needs to update CR)

After full test suite gonna add test for deprecation (looking for better wording)

bit more clean-up

Added test and fixed existing to prevent throwing deprecation

The last submitted patch, 98: 1268180-98.patch, failed testing. View results →

The test failures show it. How do we trigger warnings without causing a lot of noise for tests?

+++ b/core/lib/Drupal/Core/Render/Element/HtmlTag.php
@@ -105,7 +105,13 @@ public static function preRenderHtmlTag($element) {
-    $suffix = isset($element['#suffix']) ? $close_tag . $element['#suffix'] : $close_tag;
+    if (isset($element['#suffix'])) {
+      $suffix = $close_tag . $element['#suffix'];
+    }
+    else {
+      $suffix = $close_tag . "\n";
+      @trigger_error('Addition of newline to HTML tags is deprecated in drupal:10.2.0 and is removed from drupal:11.0.0. Set #suffix to "\\n" to keep the existing behaviour. See https://www.drupal.org/node/2742955', E_USER_DEPRECATED);
+    }

This condition needs improvement at least a global kill-switch in settings.php to enable BC mode

Wonder if we just make this change in a minor, and a change record/release note is enough. Deprecating on unset #suffix is very noisy and I think 99% of users won't care that we make this change.

#102++