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