Child content within `<d2l-alert>` is not accessible by default

[Kiefer-Co-D2L]

Regarding <d2l-alert>, Kaiju has noticed an accessibility defect (KAIJU-35) where the alert's contents cannot be tabbed through to and read by screen readers.

Kaiju has found a workaround by adding aria and role attributes to a span containing the alert's child content, but the issue can still be seen when using the alert component as described in the daylight sandbox.