Allow UiAutomation to adopt the shell permission indentity

For testing we often need to run shell commands. This can be done
today via running a shell command from an instrumentation test
started from the shell. However, this requires adding shell commands
which are not in the API contract, involve boilerplate code, require
string parsing, etc.

This change allows an instrumentation started from the shell to
adopt the shell UID permission state. As a result one can call APIs
protected by permissions normal apps cannot get by are granted to
the shell. This enables adding dedicated test APIs protected by
signatures permissions  granted to the shell.

Test: cts-tradefed run cts-dev -m CtsUiAutomationTestCases
          -t android.app.uiautomation.cts.UiAutomationTest#testAdoptShellPermissions

bug:80415658

Change-Id: I4bfd4b475225125512abf80ea98cd8fcacb6a1be