Replace use of whitelist/blacklist in \Drupal\Core\Utility\Error and its test

CR for each of these separately, or should we do a single CR for all such protected member renaming that's happening under #2993575: [meta] Remove usage of "blacklist", "whitelist", use better terms instead?

How's this?

The Drupal\Core\Utility\Error::$blacklistFunctions protected member is now called $ignoredFunctions

1. @internal

   The following parts of the code base should always be treated as internal and are not guaranteed to not change between minor versions. For patch versions we will aim to avoid any breaking changes even to @internal code unless required to fix a serious bug:

   ...

   # Protected properties
   Protected properties on a class are always considered @internal unless they're on a base class marked with @api

   -- See https://www.drupal.org/core/d8-bc-policy

   Not sure if we need BC for the property $blacklistFunctions, as no classes in contributed modules has extended it pointed by @alexpott in #3, maybe, the CR is enough. BTW, found $blacklistFunctions occurrences in the tag1quo module (http://grep.xnddx.ru/search?text=%24blacklistFunctions&filename=) , but the code is irrelevant to the class \Drupal\Core\Utility\Error.

2. +++ b/core/lib/Drupal/Core/Utility/Error.php
   @@ -19,11 +19,11 @@ class Error {
   -   * An array of blacklisted functions.
   +   * An array of ignored functions.
   
   @@ -110,9 +110,9 @@ public static function renderExceptionSafe($exception) {
   -    // information about file and line. Ignore black listed functions.
   +    // information about file and line. Ignore the ignored functions.
   

   blacklisted/black listed functions -> ignored functions, makes sense to me.

3. +++ b/core/lib/Drupal/Core/Utility/Error.php
   @@ -19,11 +19,11 @@ class Error {
   -  protected static $blacklistFunctions = ['debug', '_drupal_error_handler', '_drupal_exception_handler'];
   +  protected static $ignoredFunctions = ['debug', '_drupal_error_handler', '_drupal_exception_handler'];
   
   @@ -110,9 +110,9 @@ public static function renderExceptionSafe($exception) {
   -      (isset($backtrace[1]['function']) && in_array($backtrace[1]['function'], static::$blacklistFunctions))) {
   +      (isset($backtrace[1]['function']) && in_array($backtrace[1]['function'], static::$ignoredFunctions))) {
   
   +++ b/core/tests/Drupal/Tests/Core/Utility/ErrorTest.php
   @@ -49,7 +49,7 @@ public function providerTestGetLastCaller() {
   -    // Add blacklist functions to backtrace. They should get removed.
   +    // Add ignored functions to backtrace. They should get removed.
   

   blacklist functions -> ignored functions, not 100% sure. However, @dww is a native English speaker, this change should be good.

Thanks!