[ai-form-recognizer] Support creating composed models (Azure#12564)

* [ai-form-recognizer] Implement beginCreateComposedModel

* Compose samples

* Added a test for compose

* Recorded test for compose model

* Fixed poller to remove 'client' & ran eslint

* Updated a test to use the correct property name

* Made test skipping for AAD compose more robust

* Fixed a small bug in the samples showing 'null'

* Re-recorded compose/selection mark tests

* CHANGELOG

* Disable eslint rule no-invalid-this in formtrainingclient.spec.ts

* Fixed a playback-mode replacement

* Removed a .only

Author: witemple-msft

sdk/formrecognizer/ai-form-recognizer/CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## 3.1.0-beta.1 (Unreleased)
 
+- Added support for creating composed models through the `beginCreateComposedModel` method of `FormTrainingClient`. It accepts a list of model IDs that refer to labeled custom models that should be composed into a new model.
 - Added a `formTypeConfidence` property to `RecognizedForm` indicating the model's confidence in determining the correct form type (and therefore the correct model to use) during recognition.
 - Added a `properties` field to `CustomFormModelInfo` that may optionally contain extra properties. Currently, the only property is `isComposedModel` which will indicate whether the model is a composed model or a single trained model.
 - Added a `modelId` field to the `CustomFormSubmodel`, `TrainingDocumentInfo`, and `RecognizedForm` types containing the ID of the exact model that they are associated with (for example, in the context of a composed model, the `modelId` field can determine which specific component model is associated with the submodel, training document, or recognized form).