New incident and search modals should be mutually exclusive when opened via shortcuts

[noah-schechter]

[Not a regression] [Yes, this is an extreme edge case]

Current When opening modals via keyboard shortcut: The search modal opens above the new incident modal when the new incident modal is already open, but it doesn't close the new incident modal. This is:

• Confusing, because it's inconsistent with their behavior when opened via sidebar buttons
• Visually weird, because it doubles the intensity of the visual changes we're making to the rest of the page.

Proposed The new incident and search modals should be mutually exclusive when opened via shortcuts and sidebar; opening one modal via button or sidebar should close the other.