Lower short-circuited jumps through unified bytecode

[rogeralsing]

Summary

• lower expression bytecode JumpIfShortCircuited into unified bytecode instead of declining the shape
• preserve optional-chain short-circuit state in the unified VM so ordinary undefined and short-circuited undefined stay distinct
• refresh the unified bytecode expansion contract now that the short-circuit expression op is covered
• keep direct VM named-slot preloads from being overwritten by unrelated fallback environment slots

Verification

• rtk dotnet test tests/Asynkron.JsEngine.Tests -c Release --filter "FullyQualifiedName~UnifiedBytecodeProductionEligibilityTests.Evaluate_ObjectMethodAndAccessorLiteralShapes_AcceptAndVmDefinesProperty"
• rtk dotnet test tests/Asynkron.JsEngine.Tests -c Release --filter "FullyQualifiedNameUnifiedBytecodeProductionEligibilityTests|FullyQualifiedNameUnifiedBytecodeProductionInvocationTests|FullyQualifiedName~ExpressionProgramCoverageMapTests"
• rtk dotnet test tests/Asynkron.JsEngine.Tests -c Release --filter "FullyQualifiedNameTdzClosureTest.Debug_InnerFunctionCanWriteLetAfterInit|FullyQualifiedNameTdzClosureTest.H4_VarIsHoisted_ShouldNotThrow|FullyQualifiedNameIrLoopEnvironmentTests.LogicalCompoundAssignment_UsesLogicalAssignmentInstruction|FullyQualifiedNameIrLoopEnvironmentTests.ConditionalExpression_ReusesBranchAndDedicatedInstructionForms|FullyQualifiedName~ConstAssignmentTests.ConstAssignments_AreCaughtAsTypeErrors"
• rtk git diff --check

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