[OpenMP][OMPT] Fix `target enter data` callback ordering & reported device num

This patch fixes: https://github.com/llvm/llvm-project/issues/64738
We observed multiple issues, primarily that the `DeviceId` was reported as -1
in certain scenarios. The reason for this is simply that the device is not
initialized at that point. Hence, we need to move the RAII object creation just
after the `checkDeviceAndCtors`, closer to the actual call we want to observe.

This also solves an odering issue where one `target enter data` callback would
be executed before the `Init` callback.
Additionally, this change will also fix that the callbacks corresponding to
`enter / exit data` and `update` in conjunction with `nowait` would not result
in the emission of an OMPT callback.

Added a testcase to cover initialized device number and `omp target` constructs.

Reviewed By: dhruvachak

Differential Revision: https://reviews.llvm.org/D157605