matIcon: Use the symbol viewBox by default

[Sl1MBoy]

Feature Description

When I register an SVG icon set containing symbols I would like that matIcons utilize the viewBox from the symbol. While this PR allows us to set a viewBox value when registering the set, it will use the same value for all the symbols.

Use Case

This way we can have a resizable icon without any additional setting.

[angular-automatic-lock-bot]

This issue has been automatically locked due to inactivity.
Please file a new issue if you are encountering a similar or related problem.

Read more about our automatic conversation locking policy.

_{This action has been performed automatically by a bot.}