Handle user current arg in OverlayManager dump

Currently the OverlayManagerService adb shell command dump only allows
numeric arguments for the user. This modifies it to also allow current
as an argument, and resolves it to the current system user.

Flag: EXEMPT refactor
Bug: 377912666
Test: atest InstallOverlayTests#testAdbShellOMSInterface
Change-Id: Ia871e168eef34a7e6064ed5e0c98ca8164465e7f