fix(toolbar): input placeholders and ink need more contrast

[Splaktar]

PR Checklist

Please check that your PR fulfills the following requirements:

• The commit message follows our guidelines
• Tests for the changes have been added or this is not a bug fix / enhancement
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PR Type

What kind of change does this PR introduce?

[x] Bugfix
[ ] Enhancement
[ ] Documentation content changes
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

Inputs in toolbars aren't themed properly and don't meet a11y guidelines for contrast.

Issue Number:
Fixes #7987. This depends on #11376 being merged first.

What is the new behavior?

Inputs in toolbars are themed properly and have contrast to make them readable.

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

Before

After

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[mmalerba]

LGTM

[googlebot]

CLAs look good, thanks!

ℹ️ Googlers: Go here for more info.

[Splaktar]

PR #11953 builds upon this and improves toolbar and input theming a bit more.