fix(toolbar): md-scroll-shrink conflicts with md-select in toolbar

[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?

• On a md-select nested within a md-toolbar which has md-scroll-shrink activated,
  when onChangeScrollShrink is called, closestContent contains the md-select's md-content, which is later moved to the body, but it's already too late, scroll listeners have already been applied.
• md-scroll-shrink does not work if content is scrolled too soon after page load

Issue Number:
Fixes #10413. Closes #9871

What is the new behavior?

• md-toolbar only looks for sibling md-content elements and not md-content elements within the toolbar itself
• md-scroll-shrink works even if content is scrolled soon after page load

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

Original PR: #9856
2nd try PR: #9871

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[Splaktar]

Caretaker Note

CLA approval happened on previous PR here: #9871 (comment)

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