qml: fix the broken shadow in player view

DropShadow available in Qt5Compat does not support adjusting samples (Qt 6.2), because we do not want to compile shaders at run-time (explicit opt-out on Qt 6.7).

The default samples setting yields an inferior shadow quality compared to the pre-generated shadow image. Not only that, depending on the platform, it may appear completely bugged.

Here, this shadow is a stand-alone shadow so we do not need caching. Without caching, using pre-generated image can be justified also considering the (a)synchronoucity.

Request review @chub.