The webkit search cancel button should not be hidden

Problem/Motivation

Postponed on #2821525: Update normalize.css to the most recent version, which is also the issue where this was discovered. In that issue, Normalize.css was updated from 3.0.3 to 8.0.1. This rule was present in normalize.css 3.0.3 but has since been removed as they correctly concluded it was preventing access to legitimate functionality (and several libraries were overriding this rule because of it):

input[type="search"]::-webkit-search-cancel-button {
  -webkit-appearance: none;
 }

When this rule is removed in Drupal, however, it breaks styling for search inputs in Safari (and possibly other browsers) when using Seven, while Bartik and Umami are also changed, but it will require discussion before we can conclude if it's an acceptable change. Examples:
Bartik
With search cancel hidden, it looks like we expect

With search cancel not hidden

Seven
Is more subtle, but still changes things:
With search cancel hidden

With search cancel not hidden, the button and input top/bottom are no longer perfectly aligned

Umami
The version with the rule removed is on top. The input is slightly taller and the cancel button is slightly not aligned with the search button text.

Claro
The version with the rule removed is on the left -- the input is slightly wider as a result.

Because of these styling changes, this rule has been added back to all core themes despite its removal in normalize.css. Ideally, this rule should not be present as the search cancel button is functionality users should have access to.

Proposed resolution

- Remove instances of the rule mentioned above (it will be accompanied by a @todo for this issue).

- Correct any styling differences that can be categorized as problems due to this un-hiding the webkit search cancel button. It's possible some of these will be considered acceptable changes.

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet

The webkit search cancel button was previously not displayed by core themes. This button is now displayed and will appear in the search input when text is entered when viewed by a webkit browser that supports this functionality.