Fix completions triggered on existing private identifier property access

[andrewbranch]

Fixes #36119

[DanielRosenwasser]

@typescript-bot pack this

[typescript-bot]

Heya @DanielRosenwasser, I've started to run the tarball bundle task on this PR at 1a1a3a2. You can monitor the build here. It should now contribute to this PR's status checks.

[typescript-bot]

Hey @DanielRosenwasser, I've packed this into an installable tgz. You can install it for testing by referencing it in your package.json like so:

{
    "devDependencies": {
        "typescript": "https://typescript.visualstudio.com/cf7ac146-d525-443c-b23c-0d58337efebc/_apis/build/builds/60306/artifacts?artifactName=tgz&fileId=5B868EFA72F6A5BAE97201BB73A01EDBA9103291701C23297184A2D9E954627D02&fileName=/typescript-3.8.0-insiders.20200115.tgz"
    }
}

and then running npm install.

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There is also a playground for this build.