fix ignoring new line characters in string interpolation

[cosmicshuai]

fixes: microsoft/botbuilder-dotnet#4547

now string interpolation in adaptive expressions:

'`${hello} \n\n ${world}`'

will return:

"hello 

  world"

[coveralls]

Pull Request Test Coverage Report for Build 162888

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 9 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.07%) to 82.901%

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Files with Coverage Reduction	New Missed Lines	%
libraries/botframework-streaming/src/webSocket/webSocketTransport.ts	2	80.65%
libraries/botframework-streaming/src/webSocket/webSocketServer.ts	7	66.67%

Totals
Change from base Build 162883:	-0.07%
Covered Lines:	15168
Relevant Lines:	17405

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💛 - Coveralls