Introduce support for custom reason in @DisabledInAotMode

[sbrannen]

@DisabledInAotMode has a default disabled reason but currently does not provide a mechanism to add a custom reason.

However, almost all condition annotations provided by JUnit Jupiter (@Disabled, @DisabledOnOs, @DisabledForJreRange, etc.) provide an attribute to supply a custom reason. Thus, users of those annotations would likely expect @DisabledInAotMode to support a custom reason as well.

In addition, we already have over 50 places in our own test suite where we could make use of this feature.