fix(theming): Adjust status colors and make dark theme fully accessible

[susnux]

• ⚠️ This is chained onto fix(theming): Adjust theming util to calculate primary element color based on WCAG color contrast #42285 which needs to be merged first!

Summary

This is based on #42285 which provides initial support for WCAG contrast calculation and unit testing the themes.

This fixes two problem:

1. The status colors are still not fully accessible especially on blurry background
2. The dark theme is not fully accessible on all supported color + background combinations

besides fixing the issues this also adds a unit test for the dark theme to get notified in case of errors.

For the dark theme all status colors needed to a bit more brighter:

For the default theme warning and error needed to be adjusted:

error	warning

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[susnux]

/backport to stable28

[JuliaKirschenheuter]

🥳 great work! Tested on several places, all good until now

[emoral435]

LGTM as well :)

[backportbot-nextcloud]

The backport to stable28 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable28
git pull origin stable28

# Create the new backport branch
git checkout -b fix/foo-stable28

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts. Resolve them.
git cherry-pick abc123

# Push the cherry pick commit to the remote repository and open a pull request
git push origin fix/foo-stable28

Error: Unknown error

More info at https://docs.nextcloud.com/server/latest/developer_manual/getting_started/development_process.html#manual-backport

[susnux]

/backport to stable28

[backportbot-nextcloud]

The backport to stable28 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable28
git pull origin stable28

# Create the new backport branch
git checkout -b fix/foo-stable28

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts. Resolve them.
git cherry-pick abc123

# Push the cherry pick commit to the remote repository and open a pull request
git push origin fix/foo-stable28

Error: Unknown error

More info at https://docs.nextcloud.com/server/latest/developer_manual/getting_started/development_process.html#manual-backport

[ShGKme]

Warning is not contrast with text

[susnux]

Warning is not contrast with text

Known limitation of dark theme but warning background with text is also deprecated and shall not be used by design team.
So we can fix this on components, but it simply should only be used for graphical elements and text should be color warning text on default background.