Release v4.121.0

Added

• $identity.<property> reads the caller wherever an expression is accepted, as a shorter root for $context.identity.<property>. It names the same properties (id, name, userName, isAuthenticated, roles, claims.<name>), warns with PLAY0155 on an unknown property, and compiles to exactly the same executable model as the $context.identity spelling. $context.identity keeps working unchanged. Both editors highlight, complete and check the new root (part of #119)