Fix getOffsetToReveal for growthDirection reversed and AxisDirection down or right

[tarobins]

Description

Added the same differentiation for computing offset based on growthDirection to the AxisDirection.down and .right cases that existed for .up and .left cases.

Related Issues

#38301

Tests

I added the following tests:

Viewport getOffsetToReveal Sliver - up - reverse growth
Viewport getOffsetToReveal Sliver - left - reverse growth

both based on

Viewport getOffsetToReveal Sliver - up
Viewport getOffsetToReveal Sliver - left

respectively, but with reverse growth slivers.

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[goderbauer]

LGTM