Fix Cosmos nesting problem

[v-kydela]

Fixes #3126

Description

Some customers experienced cryptic error messages when using Cosmos. We discovered that deeply nested data was the culprit, so I've added new error messages to help customers who encounter this problem in the future.

Specific Changes

• Two new tests have been added to cosmosDbPartitionedStorage.test.js
• CosmosDbPartitionedStorage checks the nesting depth when a Cosmos exception is thrown during a write operation
• Some code cleanup has been applied to cosmosDbPartitionedStorage.ts and cosmosDbPartitionedStorage.test.js

Testing

Included. Note that waterfall dialogs break recorded tests by generating random instance ID's, and mockHelper.js is designed to fix the test data by looking for waterfall dialogs in the root dialog stack. It is not designed to look for waterfall dialogs inside component dialogs, so it cannot automatically fix the recorded test data for the dialog nesting test. Rather than fixing mockHelper.js or trying some type of non-waterfall dialog, I decided to edit the test data manually because I am told we will be moving to a new testing system soon. This was the simplest solution, but it means that it will need to be manually edited again if new test data is recorded for the dialog nesting test.

[coveralls]

Pull Request Test Coverage Report for Build 472780698

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 22 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.008%) to 84.367%

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Files with Coverage Reduction	New Missed Lines	%
libraries/botbuilder-lg/src/templateExtensions.ts	1	84.48%
libraries/botbuilder-azure/src/cosmosDbPartitionedStorage.ts	21	77.07%

Totals
Change from base Build 472682418:	0.008%
Covered Lines:	17744
Relevant Lines:	20090

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💛 - Coveralls

[joshgummersall]

let preferred to var.

[joshgummersall]

@v-kydela I accidentally approved & merged before you had a chance to amend the var usage. I handled that and added a lint rule that will complain about var in the future (#3179).