…ound on dark mode

… into FW-5721

Issue number: N/A
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<!-- Please do not submit updates to dependencies unless it fixes an
issue. -->
<!-- Please try to limit your pull request to one type (bugfix, feature,
etc). Submit multiple pull requests if needed. -->
## What is the current behavior?
<!-- Please describe the current behavior that you are modifying. -->
The toolbar `basic` test only checks light theme. Dark theme coverage is
required to test against the bug fixed in
#29216.
## What is the new behavior?
<!-- Please describe the behavior or changes that are being added by
this PR. -->
Dark theme coverage added. This required converting the test to
`page.setContent` instead of `page.goto`, so I went ahead and split the
captured toolbars into multiple tests, including some cleanup of the
test content. Since this included changes across many different tests,
even ones not strictly related to the bug, this work has been split into
a separate PR.
## Does this introduce a breaking change?
- [ ] Yes
- [x] No
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  2. Update the BREAKING.md file with the breaking change.
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## Other information
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screenshots of how the component looks before and after the change. -->
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Co-authored-by: ionitron <hi@ionicframework.com>