[FormRecognizer] add a test for the multiple page receipt scenario

[jeremymeng]

Use the pdf file from https://github.com/Azure/azure-sdk-for-python/blob/master/sdk/formrecognizer/azure-ai-formrecognizer/tests/sample_forms/forms/multipage_invoice1.pdf

Currently JS code doesn't handle the empty document result well.

• add test
• fix issue
• once the service fix a regression on receipt total, we can add verification of that.

[willmtemple]

Service regression on the receipt method (undefined valueNumber) has not been resolved, but has been removed as a release blocker for GA.

[witemple-msft]

We've decided not to make assertions on values in some circumstances, as they come from AI models and so have some amount of inherent uncertainty/instability. This is an ongoing discussion in the Form Recognizer team, so I'm going to close this issue and may open another when there's some concrete action to take.