Compress HackEmit* guards, add DemitLdfld/Stfld/Ldsfld/Ldflda helpers, update call sites, compact comments

Agent-Logs-Url: https://github.com/dadhi/FastExpressionCompiler/sessions/9613f5f4-79a9-4a47-ad46-14c291909fb4

Co-authored-by: dadhi <39516+dadhi@users.noreply.github.com>

Author: Copilot