Remove calls to deprecated methods (checkPlain and format_date)

Problem/Motivation

Spotted use of some deprecated methods during module upgrade.

Proposed resolution

Changes in drupalmoduleupgrader.grep.yml:

function_calls:
  check_plain: '\Drupal\Component\Utility\SafeMarkup::checkPlain'

to

function_calls:
  check_plain: '\Drupal\Component\Utility\Html::escape'

However this may cause "double escaping" as highlighted here: #2549395: SafeMarkup methods are removed in "Escaping markup" - "Twig" section.

Remaining tasks

1. Is double escaping above ok or does it need an associated comment and link to this change record?

2. Should format_date be changed to use a formatter with the same arguments rather than the advised service from format_date documentation.

i.e.

format_interval: '\Drupal::service("date.formatter")->formatInterval'

or

format_interval: '\Drupal\Core\Datetime\DateFormatter::format'

The latter has the same arguments and seems the right choice to me. Does this require a comment in code also to recommend using the service?

User interface changes

N/A

API changes

Depends on choices in the "Remaining Tasks" above.

Data model changes

N/A (None that I'm aware of)

Original report by [mccrodp]

N/A