feat(core): use CSS variables for font (sizes) on textfields

[loxy]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows Conventional Commits
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Refactoring
• Code style update
• Build or CI related changes
• Documentation content changes

What is the current behavior?

Closes #1471

What is the new behavior?

The textfield mixins are now using corresponding CSS variables instead of hard coded values.

Does this PR introduce a breaking change?

• Yes
• No

[lumberjack-bot]

Pull request was closed ✔️

All saved screenshots (for current PR) were deleted 🗑️

[codecov]

Codecov Report

Merging #1494 (aae30d3) into main (a075a54) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1494   +/-   ##
=======================================
  Coverage   64.32%   64.32%           
=======================================
  Files         850      850           
  Lines        9416     9416           
  Branches     1838     1838           
=======================================
  Hits         6057     6057           
  Misses       2920     2920           
  Partials      439      439           

Flag	Coverage Δ
addon-charts	74.69% <ø> (ø)
addon-doc	25.84% <ø> (ø)
addon-editor	46.05% <ø> (ø)
addon-mobile	∅ <ø> (∅)
addon-table	81.39% <ø> (ø)
addon-tablebars	∅ <ø> (∅)
cdk	82.75% <ø> (ø)
core	68.98% <ø> (ø)
kit	62.17% <ø> (ø)
summary	64.32% <ø> (ø)

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[loxy]

I think the failing screenshot test come from switching the font-size from 0.69rem to 0.6875rem (--tui-font-text-xs)

[well-done-bot]