[PORT] Fully respect the original input in a string interpolation context

[Danieladu]

Original issue: microsoft/botbuilder-dotnet#4902
C# PR: microsoft/botbuilder-dotnet#4906

Description

Originally, the string interpolation would over escape some string or character. For example:

Expression.Parse(" `\\r\\n` ").TryEvaluate(null).value -> [CR][LF]

Expression SDK would escape "\r\n" again, and convert them into a newline.

The string interpolation should respect the original input. So, the expected result is string \r\n, but not [CR][LF]

But there are still two special cases.
One is "$" and the other one is "`". Example:

Expression.Parse(" `${12}\\${34}` ").TryEvaluate(null).value   -> 12${34}
Expression.Parse(" `\\`` ").TryEvaluate(null).value   -> `