refactor expander

[feich-ms]

Fixes #3523 microsoft/botbuilder-dotnet#3523
Fixes #2014

Description

Refactor lg expander to support full functions of LG and fix several issues such as excape, double quotation. Also change the return type from string array to object array.

Specific Changes

• Support all kinds of LG functions

• Discard the 'builtin.' prefix

• Fix escape issues, including double quotation, escape character

• change return type from string array to object array

Testing

Corresponding test cases are added in lg.test.js

[coveralls]

Pull Request Test Coverage Report for Build 119434

• 15 of 15 (100.0%) changed or added relevant lines in 1 file are covered.
• 9 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.1%) to 67.127%

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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 119067:	0.1%
Covered Lines:	10263
Relevant Lines:	14465

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💛 - Coveralls