mat-icons as a matSuffix or matPrefix in a mat-form-field do not match the material spec

[adamdport]

Bug, feature request, or proposal:

bug

What is the expected behavior?

mat-icons used as a matPrefix or matSuffix should vertically align with the input text/placeholder

What is the current behavior?

icons are positioned too high

CodePen and steps to reproduce the issue:

https://stackblitz.com/edit/angular-material2-issue-jrwkpg

What is the use-case or motivation for changing an existing behavior?

It doesn't look good

Which versions of AngularJS, Material, OS, and browsers are affected?

"@angular/core": "5.2.10",
"@angular/material": "5.2.5",

Is there anything else we should know? Stack Traces, Screenshots, etc.

The specs show that icons should be vertically aligned with the text

[josephperrott]

Duplicate of #10093

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