Refactor FlagTestBase::createFlag() to reduce code in other tests

I think this change is worthwhile.

A few minor things

1) entiyManager is deprecated

the replacement is \Drupal::service('entity_type.bundle.info')

2) I want to lock down a few parameter input type that we are touching.
In short we should prefix inputs like $edit with array.
This could be done to other methods in the class .. but hey that is for another issue.

3) When I first glanced at createFlagFromArray() my first impression was ok cool that is a pattern I recognise.
I wonder if it is whitelisting key values pairs or if I am free to add values outside the default.

I want the annotations to try and answer that question without the next reader to having to inspect the code, so I added an extra sentence.

1. +++ b/src/Tests/FlagTestBase.php
   @@ -72,35 +72,77 @@ abstract class FlagTestBase extends WebTestBase {
   +  protected function createFlag($entity_type = 'node', array $bundles = [], $link_type = 'reload') {
   ...
   +  protected function createGlobalFlag($entity_type = 'node', array $bundles = [], $link_type = 'reload') {
   

   Logically, if we have both of these, then it should be create(Global|Personal)Flag.

2. +++ b/src/Tests/FlagTestBase.php
   @@ -72,35 +72,77 @@ abstract class FlagTestBase extends WebTestBase {
   +  protected function createFlagFromArray(array $edit) {
   

   I considered adding something like this when I was working on tests last week.

   What made me reconsider was the thought that: a) it doesn't save on that much code, and b) it means that when you see createFlagFromArray([STUFF]) in a test, you then have to go and look in the base class to see what the defaults are for the properties not in STUFF. I am concerned that will make tests harder to read and understand.