feat: Update colors for warnings in status-related components

[jperals]

Description

(Updated replica of #1231)

A visual update to components that use "warning" status: status indicator, alert, flashbar, and code editor.

Currently, warning status doesn't have a dedicated color and instead either uses warning or info colors. This change now introduces a new set of yellow tones for warning specifically.

Design POC is Adam.

Related links, issue #, if available: AWSUI-8420, Zb5hAZRq0yk8/Warning-Colour-Update

How has this been tested?

• Added permutations for visual regression testing
• Reviewed BackstopJS diffs
• Reviewed by visual design and UX design

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates.
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md.
• Changes do not include unsupported browser features, see CONTRIBUTING.md.
• Changes were manually tested for accessibility, see accessibility guidelines.

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function.

Testing

• Changes are covered with new/existing unit tests?
• Changes are covered with new/existing integration tests?

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[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (d84a8e1) 93.47% compared to head (b16ff3b) 93.47%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1340   +/-   ##
=======================================
  Coverage   93.47%   93.47%           
=======================================
  Files         623      623           
  Lines       16770    16772    +2     
  Branches     5551     5551           
=======================================
+ Hits        15675    15677    +2     
  Misses       1022     1022           
  Partials       73       73           

Files Changed	Coverage Δ
src/flashbar/utils.ts	97.95% <ø> (ø)
src/flashbar/collapsible-flashbar.tsx	98.02% <100.00%> (+0.02%)	⬆️
src/flashbar/flash.tsx	100.00% <100.00%> (ø)
src/flashbar/non-collapsible-flashbar.tsx	100.00% <100.00%> (ø)

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[fralongo]

Why do we need to expose this token? It is already themeable by theming the colorTextNotificationDefault in the newly introduced flashvar-warning context

[jperals]

I think you're right, removed the token from the metadata.

[johannes-weber]

The changes are looking good to me.
When checking the visual differences, I saw the Code Editor does not have a permutation page. Do you know if this is by purpose? If not, I think this PR is a good opportunity for adding the permutation page.

[jperals]

I don't know if the Code editor not having a permutations page is by purpose. I didn't add coverage for Code editor because I noticed that the warning icon is covered by this existing page, even though it could be a good idea to change its name and title (because they suggest that the code editor doesn't show any warning, though it does).

It's true that having a permutations page for Code editor would help catch potential regressions at the PR stage. But I think I'd rather do that separately. So in short I'd do the following:

1. Open a PR to add permutations page for Code editor
2. Change name and title of /light/code-editor/with-errors-no-warnings, either in this PR or in the one mentioned previously