Use the app request aspect ratio for Task letterboxing

Before, when app requests fix orientation with aspect ratio, it will
first be letterboxed at Task level with display ratio, and then be
letterboxed at Activity level with request ratio, which may become too
small (fill neither of display width and height).

This change is to have Task level letterboxing use the app request
aspect ratio (if set) instead of display ratio.

Bug: 170725334
Bug: 155431879
Test: atest WmTests:SizeCompatTests
Test: manual: adb shell wm set-ignore-orientation-request true
Change-Id: I568db28125fa11c2a78ff4d6930abb49ca3fffe8