Table Sort Indicator Style Update

[antonellasevero]

Problem/Motivation

Recent interviews and research exposed pain points around Drupal's admin experience of looking and feeling dated, especially compared to our competitors, and universally cited that choosing a more modern-looking admin theme instantly led to Drupal being better-perceived by said users.
There was an amazing community effort to Create a Style Guide For Seven that vastly improved its look + feel compared to the original, but Design best practices and Drupal functionality have moved on since then.

Proposed resolution

Implement new table sort indicator styles to create a favorable first impression of Drupal for evaluators and a better user experience for site authors. No functional differences.

Specs:
https://www.figma.com/file/OqWgzAluHtsOd5uwm1lubFeH/Design-system?node-id=1646%3A1507

General specs:

Color palette

Remaining tasks

• Update patch styling to include time inputs
• Accessibility review
• LTR review (Left to right)

User interface changes

All table sort indicator styles will be changed, no functional differences.

Test Pages

/admin/content
/admin/content/files
/admin/content/comment
/admin/people

[kiran-kadam911]

Taking this up.