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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Inizia dalla riproduzione StackBlitz collegata, in particolare da material-module.ts riga 48, e alterna MatFormFieldDefaultOptions tra legacy e standard. Confronta il valore delle opzioni del paginator con la relativa freccia e traccia lo stile del select del paginator utilizzato dalla riproduzione. Il lavoro è completato quando il valore è allineato verticalmente con la freccia nell’aspetto standard senza compromettere l’aspetto legacy.

Scritto dal modello di indicizzazione a partire dal testo della issue.