Fix IntDef's usages in the platform Transitions

Bug: 68490704

1) Add annotation in some places where it was missed: constructors of Fade and Slide
2) Add Fade.IN and Fade.OUT into a set of allowed values for Visibility.MODE IntDef. Without it Lint will false alarm on this line:
new Fade().setMode(Fade.IN);
It should be allowed as Fade.IN is just a proxy value for Visibility.MODE_IN.

Test: n/a
Change-Id: I56d8ba5f49b1cf8f6a61357f58ac76312e7cf037