fix(input): placeholder hidden when there is also a label on IE11

[Splaktar]

PR Checklist

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• The commit message follows our guidelines
• Tests for the changes have been added or this is not a bug fix / enhancement
• Docs have been added, updated, or were not required

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?

If a md-input has both a placeholder and a label, the placeholder is invisible on IE11.

Issue Number:
Fixes #11668

What is the new behavior?

If a md-input has both a placeholder and a label, the placeholder is visible on IE11.

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

Verified manually in IE11 on Windows 10. No unit tests added as we don't run them against IE11.
Also verified by the reporter in #11668 (comment).