Add JMESPath support for DynamoDB's TransactGetItem

[Velfi]

Currently, trying to build the model will result in:

Projection dynamodb failed: software.amazon.smithy.rust.codegen.client.smithy.generators.waiters.UnsupportedJmesPathException: Only projection expressions with flattens are supported by smithy-rs
Expression: "TransactItems"[*]."Get"."TableName"
software.amazon.smithy.rust.codegen.client.smithy.generators.waiters.UnsupportedJmesPathException: Only projection expressions with flattens are supported by smithy-rs
Expression: "TransactItems"[*]."Get"."TableName"
 at software.amazon.smithy.rust.codegen.client.smithy.generators.waiters.RustJmespathShapeTraversalGenerator.generate(RustJmespathShapeTraversalGenerator.kt:330)
 at software.amazon.smithy.rust.codegen.client.smithy.endpoint.generators.EndpointParamsInterceptorGenerator$paramSetters$1.invoke(EndpointParamsInterceptorGenerator.kt:163)
 at software.amazon.smithy.rust.codegen.client.smithy.endpoint.generators.EndpointParamsInterceptorGenerator$paramSetters$1.invoke(EndpointParamsInterceptorGenerator.kt:130)
 at software.amazon.smithy.rust.codegen.core.rustlang.RustWriter$RustSymbolFormatter.apply(RustWriter.kt:1002)
 at software.amazon.smithy.rust.codegen.core.rustlang.RustWriter$RustSymbolFormatter.apply(RustWriter.kt:971)
 at software.amazon.smithy.utils.AbstractCodeWriter.applyFormatter(AbstractCodeWriter.java:2023)
 at software.amazon.smithy.utils.CodeFormatter$Operation.lambda$formatted$1(CodeFormatter.java:108)
 at software.amazon.smithy.utils.CodeFormatter$BlockOperation$Unconditional.apply(CodeFormatter.java:228)
 at software.amazon.smithy.utils.CodeFormatter.run(CodeFormatter.java:41)
 at software.amazon.smithy.utils.AbstractCodeWriter.format(AbstractCodeWriter.java:1702)
 at software.amazon.smithy.utils.AbstractCodeWriter.write(AbstractCodeWriter.java:1761)
 at software.amazon.smithy.rust.codegen.core.rustlang.RustWriter.write(RustWriter.kt:669)
 at software.amazon.smithy.rust.codegen.core.rustlang.RustWriterKt$rustTemplate$1.invoke(RustWriter.kt:262)
 at software.amazon.smithy.rust.codegen.core.rustlang.RustWriterKt$rustTemplate$1.invoke(RustWriter.kt:261)
 at software.amazon.smithy.rust.codegen.core.rustlang.RustWriterKt.withTemplate(RustWriter.kt:120)
 at software.amazon.smithy.rust.codegen.core.rustlang.RustWriterKt.withTemplate$default(RustWriter.kt:106)
 at software.amazon.smithy.rust.codegen.core.rustlang.RustWriterKt.rustTemplate(RustWriter.kt:261)
 at software.amazon.smithy.rust.codegen.client.smithy.endpoint.generators.EndpointParamsInterceptorGenerator.render(EndpointParamsInterceptorGenerator.kt:85)
 at software.amazon.smithy.rust.codegen.client.smithy.generators.OperationGenerator.renderOperationStruct(OperationGenerator.kt:213)
 at software.amazon.smithy.rust.codegen.client.smithy.generators.OperationGenerator.renderOperation(OperationGenerator.kt:58)
 at software.amazon.smithy.rust.codegen.client.smithy.ClientCodegenVisitor$operationShape$1.invoke(ClientCodegenVisitor.kt:317)
 at software.amazon.smithy.rust.codegen.client.smithy.ClientCodegenVisitor$operationShape$1.invoke(ClientCodegenVisitor.kt:315)
 at software.amazon.smithy.rust.codegen.core.smithy.RustCrate.withModule$lambda$6(CodegenDelegator.kt:211)
 at software.amazon.smithy.codegen.core.WriterDelegator.useFileWriter(WriterDelegator.java:175)
 at software.amazon.smithy.rust.codegen.core.smithy.RustCrate.withModule(CodegenDelegator.kt:210)
 at software.amazon.smithy.rust.codegen.core.smithy.RustCrate.useShapeWriter(CodegenDelegator.kt:109)
 at software.amazon.smithy.rust.codegen.client.smithy.ClientCodegenVisitor.operationShape(ClientCodegenVisitor.kt:315)
 at software.amazon.smithy.rust.codegen.client.smithy.ClientCodegenVisitor.operationShape(ClientCodegenVisitor.kt:61)
 at software.amazon.smithy.model.shapes.OperationShape.accept(OperationShape.java:87)
 at software.amazon.smithy.rust.codegen.client.smithy.ClientCodegenVisitor.execute(ClientCodegenVisitor.kt:165)
 at software.amazon.smithy.rust.codegen.client.smithy.RustClientCodegenPlugin.executeWithDecorator(RustClientCodegenPlugin.kt:79)
 at software.amazon.smithy.rust.codegen.client.testutil.ClientDecoratableBuildPlugin.execute(ClientCodegenIntegrationTest.kt:61)
 at software.amazon.smithy.build.SmithyBuildImpl.applyPlugin(SmithyBuildImpl.java:432)
 at software.amazon.smithy.build.SmithyBuildImpl.applyProjection(SmithyBuildImpl.java:364)
 at software.amazon.smithy.build.SmithyBuildImpl.executeSerialProjection(SmithyBuildImpl.java:281)
 at software.amazon.smithy.build.SmithyBuildImpl.lambda$applyAllProjections$4(SmithyBuildImpl.java:201)
 at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:183)
 at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1625)
 at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:509)
 at java.base/java.util.stream.ForEachOps$ForEachTask.compute(ForEachOps.java:290)
 at java.base/java.util.concurrent.CountedCompleter.exec(CountedCompleter.java:754)
 at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:373)
 at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1182)
 at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1655)
 at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1622)
 at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:165)
Caused by: software.amazon.smithy.rust.codegen.client.smithy.generators.waiters.UnsupportedJmesPathException: Only projection expressions with flattens are supported by smithy-rs
 at software.amazon.smithy.rust.codegen.client.smithy.generators.waiters.RustJmespathShapeTraversalGenerator.generateProjection(RustJmespathShapeTraversalGenerator.kt:664)
 at software.amazon.smithy.rust.codegen.client.smithy.generators.waiters.RustJmespathShapeTraversalGenerator.generate(RustJmespathShapeTraversalGenerator.kt:311)
 ... 45 more

Talk to Zelda for info on where to get the updated model that triggers this build failure.