UserProcessCondition Introduction.

This changelist introduces UserProcessCondition, a simple condition
that is true only when the process user handle identifier matches
the current user.

This can be used to limit execution of code to only the process ran by
the currently running user.

Test: atest UserProcessConditionTest
Bug: 261420432
Change-Id: I1efabf11b52d09833dc8a59a94b031bed682cab9