MatIconRegistry request: allow registering multiple default font set classes

[kuhnroyal]

Bug, feature request, or proposal:

Request

What is the expected behavior?

MatIconRegistry.setDefaultFontSetClass to accept multiple css classes

What is the current behavior?

MatIconRegistry.setDefaultFontSetClass accepts only one class

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

Some font sets require multiple classes that are tiresome to repeat on all icons.

For example: MatIconRegistry.setDefaultFontSetClasses("mdi", "mdi-48px") would be nice to have.