Bind function to class instance in middleware

[MikhailArkhipov]

For #9096
Haven't found tests for this specific class.

• Pull request represents a single change (i.e. not fixing disparate/unrelated things in a single PR)
• Title summarizes what is changing
• Has a news entry file (remember to thank yourself!)
• Appropriate comments and documentation strings in the code
  - [ ] Has sufficient logging.
  - [ ] Has telemetry for enhancements.
  - [ ] Unit tests & system/integration tests are added/updated
  - [ ] Test plan is updated as appropriate
  - [ ] package-lock.json has been regenerated by running npm install (if dependencies have changed)
  - [ ] The wiki is updated with any design decisions/details.

[codecov-io]

Codecov Report

Merging #9109 into master will decrease coverage by 0.04%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #9109      +/-   ##
==========================================
- Coverage   57.11%   57.07%   -0.05%     
==========================================
  Files         551      551              
  Lines       29144    29176      +32     
  Branches     4404     4414      +10     
==========================================
+ Hits        16646    16652       +6     
- Misses      11592    11614      +22     
- Partials      906      910       +4

Impacted Files	Coverage Δ
...ivation/languageServer/languageClientMiddleware.ts	8.1% <100%> (+1.25%)	⬆️
...ient/datascience/jupyter/kernels/kernelSelector.ts	78.94% <0%> (-8.01%)	⬇️
...nt/datascience/jupyter/kernels/kernelSelections.ts	92.64% <0%> (-1.01%)	⬇️
...lient/datascience/jupyter/jupyterSessionManager.ts	9.75% <0%> (-0.78%)	⬇️
src/client/datascience/jupyter/jupyterSession.ts	6.62% <0%> (-0.15%)	⬇️
.../datascience/interactive-common/interactiveBase.ts	18.32% <0%> (-0.03%)	⬇️
...ient/datascience/interactive-ipynb/nativeEditor.ts	53.84% <0%> (ø)	⬆️
src/client/datascience/types.ts	100% <0%> (ø)	⬆️
src/client/datascience/jupyter/notebookStarter.ts	71.54% <0%> (+0.57%)	⬆️
src/datascience-ui/react-common/postOffice.ts	4.68% <0%> (+1.05%)	⬆️

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