Updating code finder to better work with multi line snippets

[edkazcarlson-ms]

Previously our code finder had only been used with single line snippets. However due to new scenarios, we are encountering snippets that are multi line and so we have to update the code finder algorithm to be more resistant to the different line endings (ex: \r\n vs \r vs \n) as well as modify the ending line number so the highlight spans the correct number of lines.

[edkazcarlson-ms]

@EasyRhinoMSFT / @yongyan-gh just want to make sure this PR doesn't get buried