Open mutexes with explicit rights through MutexAcl

Opt-in Windows port of resolved Mutex.OpenExisting(string,MutexRights) to MutexAcl.OpenExisting, preserving argument nodes/order and nullable-call diagnostics, requested rights, result and surrounding catch/ownership policy. Add System.Threading.AccessControl 6.0.0 when absent in the owning modeled project during the same run. Skip known overlong literal/constant-allocation names, user-defined name conversions, other overloads/APIs, named/commented calls, deferred contexts and unsafe conditional snapshots. No ACL selection, Framework CAS/runtime-validation/native-failure emulation. Standalone, outside version composites.