Route optional named deletes through unified bytecode

[rogeralsing]

Summary

• admit optional named property deletes such as delete box?.value and delete box.child?.value in production unified bytecode
• add the matching compiler lowering for the nullish-to-true delete branch
• update tests/docs so optional named deletes are no longer listed as optional-chain declines

Tests

• rtk dotnet test tests/Asynkron.JsEngine.Tests -c Release --filter "FullyQualifiedNameUnifiedBytecodeProductionEligibilityTests.Evaluate_OptionalNamedPropertyDeleteCandidate_AcceptsOwnedPropertyOpcodes|FullyQualifiedNameUnifiedBytecodeProductionEligibilityTests.Evaluate_UnsupportedOptionalComputedPropertyDeleteNeighbor_DeclinesWithExplicitCode|FullyQualifiedNameUnifiedBytecodeProductionInvocationTests.OptionalNamedPropertyDelete_UsesUnifiedBytecodeProductionFastPath|FullyQualifiedNameExpressionProgramLoweringTests.ReturnInstruction_DeleteOptionalNamedProperty_IsLoweredToExpressionProgram|FullyQualifiedNameAstFreeExecutionAssertionTests.AssertNoAstEvaluation_Enabled_AllowsDeleteOptionalNamedPropertyExecution|FullyQualifiedNameExecutionPlanDiagnosticsTests|FullyQualifiedName~ExpressionProgramCoverageMapTests.UnifiedBytecodeExpansionContract_ListsRequiredHeadingsAndCurrentEnums"
• rtk dotnet test tests/Asynkron.JsEngine.Tests -c Release --filter "FullyQualifiedNameUnifiedBytecodeProductionEligibilityTests|FullyQualifiedNameUnifiedBytecodeProductionInvocationTests|FullyQualifiedNameExpressionProgramLoweringTests|FullyQualifiedNameAstFreeExecutionAssertionTests|FullyQualifiedNameExpressionProgramCoverageMapTests|FullyQualifiedNameDeleteOperatorTests"
• rtk dotnet build src/Asynkron.JsEngine/Asynkron.JsEngine.csproj -c Release
• rtk rg "EvaluateExpression(|ProfileEvaluateExpression(" src/Asynkron.JsEngine/Ast/TypedAstEvaluator.ExecutionPlanRunner*
• rtk git diff --check

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