Use insetsRoundedCornerFrame to identify taskbar insets source

Previously, many places considered that the insets source with
ITYPE_EXTRA_NAVIGATION_BAR were provided by taskbar, which were
inaccurate, because ITYPE_EXTRA_NAVIGATION_BAR can be provided by other
sources. Also, we are going to remove internal insets types.

Thus, this CL uses InsetsSource#insetsRoundedCornerFrame to identify
expended taskbar instead, and we don't need to check the height of
taskbar anymore.

Bug: 234093736
Test: atest LetterboxUiControllerTest SizeCompatTests
Change-Id: I5561cade375a326f91a252b98d37d0950b25e00f