Fix deadlock between WMGlobal and WMS

In the system server, there may be a deadlock between WMGlobal and WMS
A possible scenario is:
WMS holds globalLock and call WMGlobal#getWindowManagerService,
which required to lock WMGlobal instance, while the other compnent
holds WMGlobal and call WMS API directly without binder call,
which requires WM gobalLock.

This CL sets WMS for system proces. In this way,
WMGlobal#getWindowManagerService could be used direcly without holding
WMGlobal instance and prevent deadlock.

Test: atest WmTests
Bug: 320848325
Change-Id: I2617d4139d4305161d6712d92a90fd9207d8227c