Do not toggle expansion panel on Enter or Space if Ctrl is pressed

[AlexKichkailo]

Bug, feature request, or proposal:

Proposal

What is the expected behavior?

ctrl + enter does not toggle expansion panel

What is the current behavior?

ctrl + enter toggles expansion panel

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

Ability to implement global shortcuts for the application which often use the Ctrl key

Which versions of Angular, Material, OS, TypeScript, browsers are affected?

angular 7.0.0, material 7.0.0

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