Prioritize checks in canDreamLocked when device is kept awake

Previously, the canDreamLocked function would immediately return true if
the device was kept awake, bypassing other crucial checks like whether
the device is powered. This could lead to unintended behaviors, such as
starting a dream even when the device was not powered but the proximity
sensor returned a positive value.

This change modifies canDreamLocked to ensure that all relevant
condition checks are evaluated *before* allowing a dream to start.

Test: atest PowerManagerServiceTest
Test: manually tested dream starting while powered and not powered
Bug: 404968947
Flag: EXEMPT bugfix
Change-Id: I5c3f529db95e9a2f006e600ddea24f20a182a3fc