[flexiglass] Rename isShadeLayoutWide and flip its meaning.

The new name, `isFullWidthShade`, is consistent with the established
notion of "full width shade" in legacy code. Moreover, it more
accurately represents the divergence in behavior between this value and
`isWideScreen` (namely, on tablets devices in portrait orientation).

Fix: 354926927
Bug: 411365508
Test: Updated all affected unit tests.
Flag: com.android.systemui.scene_container
Change-Id: I08a9988a9bb7cdcdaea6819c1b2f7ae5afff2c18