HttpKernelUiHelperTrait needs to call Html::resetSeenIds() after a request

Problem/Motivation

Just found this while converting a contrib test where the assertions were getting page elements using CSS IDs, and those IDs were being made in the SUT using \Drupal\Component\Utility\Html.

HttpKernelUiHelperTrait needs to call Html::resetSeenIds() after a request (or we need to fix \Drupal\Component\Utility\Html to it works for this and for persistent servers).

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

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