Use GetCurrentMethod to get the current method when tracing

The current method is passed in a register and we can use the
GetCurrentMethod as an input to the method entry / exit hooks. In most
cases we may just have the current method in the register on method
entry.

Bug: 259258187
Test: art/test.py
Change-Id: Iea75f41b0ec5ebbc2aef857c84f39846b594e8e7