[Symfony 5] Using the "Symfony\Component\Validator\Constraints\Length" constraint with the "min" option without setting the "allowEmptyString" one is deprecated

Sorry for the delay. I'm going to try to do this one now.

Thanks for the patch.

1) Reviewed the 9.0 dev codebase for the use of:

    ...
    'Length' => ['min'...
    ...

for Constraints. The only ones with 'Length' set are:

• core/tests/Drupal/KernelTests/Core/TypedData/TypedDataTest.php
• core/lib/Drupal/Core/Field/Plugin/Field/FieldType/EmailItem.php
• core/lib/Drupal/Core/Field/Plugin/Field/FieldType/StringItem.php
• core/modules/options/src/Plugin/Field/FieldType/ListStringItem.php
• core/modules/telephone/src/Plugin/Field/FieldType/TelephoneItem.php
• core/modules/text/src/Plugin/Field/FieldType/TextItem.php
• core/lib/Drupal/Core/Field/Plugin/Field/FieldType/LanguageItem.php

but only TypedDataTest.php has min set. The rest are using max.

Looked for allowEmptyString in the code and it was only in DeprecationListenerTrait.php.

2) Since this is for Symfony 5 and the deprecation message states:

"In 5.0, it will become optional and default to false."

then adding:

'allowEmptyString' => FALSE

shouldn't be needed though it is good to have there since it helps document what's needed if it should be set to TRUE.

3) Patch applies cleanly:

[mac:kristen:drupal-9.0.x-dev]$ patch -p1 < 3117863.patch 
patching file core/tests/Drupal/KernelTests/Core/TypedData/TypedDataTest.php
patching file core/tests/Drupal/Tests/Listeners/DeprecationListenerTrait.php
Hunk #1 succeeded at 162 (offset -9 lines).

4) Not sure there is anything that can be manually tested so marking RTBC.

Committed c609c06 and pushed to 9.1.x, cherry-picked to 9.0.x. Thanks!