[OpenMP] Unify omptarget API and usage wrt. `__tgt_async_info`

[OpenMP] Unify omptarget API and usage wrt. `__tgt_async_info`

This patch unifies our libomptarget API in two ways:
  - always pass a `__tgt_async_info` object, the Queue member decides if
    it is in use or not.
  - (almost) always synchronize in the interface layer and not in the
    omptarget layer.

A side effect is that we now put all constructor and static initializer
kernels in a stream too, if the device utilizes `__tgt_async_info`.

The patch contains a TODO which can be addressed as we add support for
asynchronous malloc and free in the plugin API. This is the only
`synchronizeAsyncInfo` left in the omptarget layer.

Site note: On a V100 system the GridMini performance for small sizes
more than doubled.

Reviewed By: tianshilei1992

Differential Revision: https://reviews.llvm.org/D96379