port: [#6354] isMatch adaptive expression returns error when value is null or empty string (#6426)

[ceciliaavila]

Fixes #4310

Description

This PR ports the changes in PR#6426 to fix the error in the isMatch built-in function when the value is null or an empty string.

Specific Changes

• Updated the IsMatch built-in function to handle empty strings and null values by the evaluator.
• Added 2 new unit tests for empty string and null values for the IsMatch function.

Testing

Here we can see the new unit tests passing after the changes.

[coveralls]

Pull Request Test Coverage Report for Build 3245014103

• 4 of 4 (100.0%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.004%) to 84.617%

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

Totals
Change from base Build 3206725406:	0.004%
Covered Lines:	19922
Relevant Lines:	22305

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💛 - Coveralls