Refactor entertainer invented logic

Remove hard dependency on scenery window by calling a new is scenery set invented function. I don't think this the performance is any worse as it called init_scenery anyway for every call to get_available_entertainers.

Regression caused by multiple refactor commits. Track type and sequence was being retrieved from the entrance element instead of the track element in sub_6CB945.

Also fixes #6690.

Issue caused by using tile_element_get_type() where track_element_get_type was intended.

Every SCENERY_GHOST_FLAG_X is connected with its respective
SCENERY_TYPE_xxx flag

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