Paginator: options list visually inconsistent for legacy and standard appearance

#### Bug, feature request, or proposal:
When defining globally the appearance of the app form-fields as `standard` (via `MatFormFieldDefaultOptions`), the paginator options list value is not vertically aligned with its arrow.
When using `legacy`, (visually) everything works as expected.
On a regular `mat-form-field`, this inconsistency isn't as noticeable, probably because the font size is larger than the one used on the paginator.

#### What is the expected behavior?
Paginator options (select element) should have its value aligned with the arrow, when using `standard` appearance.

#### What is the current behavior?
Paginator options' (select element) value is not vertically aligned with the arrow.

#### What are the steps to reproduce?
https://stackblitz.com/edit/angular-cqtqvd-zwpq9y?file=material-module.ts
On the `material-module.ts` file, go to line 48 and switch the property value between 'legacy' and 'standard'.

#### What is the use-case or motivation for changing an existing behavior?
Visual inconsistency when using the 'standard' appearance.

#### Which versions of Angular, Material, OS, TypeScript, browsers are affected?
Only noticed on Angular 7 and Material 7.0.2, but this could probably affect previous versions.

#### Is there anything else we should know?
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Start with the linked StackBlitz reproduction, especially material-module.ts line 48, and switch MatFormFieldDefaultOptions between legacy and standard. Compare the paginator options value with its arrow and trace the paginator select styling used by the reproduction. Done means the value is vertically aligned with the arrow under standard appearance without breaking legacy appearance.

Written by the indexing model from the issue text.