Ignore languageServer files from vsix

[DonJayamanne]

Fixes #2150

This pull request:

• Has a title summarizes what is changing
• Includes a news entry file (remember to thank yourself!)
• Has unit tests & code coverage is not adversely affected (within reason)
• Works on all actively maintained versions of Python (e.g. Python 2.7 & the latest Python 3 release)
• Works on Windows 10, macOS, and Linux (e.g. considered file system case-sensitivity)

[codecov]

Codecov Report

Merging #2152 into master will increase coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2152      +/-   ##
==========================================
+ Coverage   79.86%   79.88%   +0.02%     
==========================================
  Files         308      308              
  Lines       14176    14176              
  Branches     2520     2520              
==========================================
+ Hits        11321    11324       +3     
+ Misses       2843     2840       -3     
  Partials       12       12

Flag	Coverage Δ
#MacOS	73.92% <ø> (ø)	⬆️
#Windows	74.06% <ø> (ø)	⬆️

Impacted Files	Coverage Δ
...rc/client/debugger/PythonProcessCallbackHandler.ts	68.42% <0%> (-0.33%)	⬇️
src/client/providers/jediProxy.ts	80% <0%> (+0.22%)	⬆️
src/client/debugger/Main.ts	67.16% <0%> (+0.24%)	⬆️
src/client/debugger/PythonProcess.ts	59.16% <0%> (+0.83%)	⬆️

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