Pass plugin information through to languages-main

[JPinkney]

What it does

This PR passes some plugin info through to languages-main and establishes a map that allows one to get a handle for a specific vscode extension's language server call.

An example of this map is:

{
    "redhat.vscode-yaml": {
        "completion": 0,
        "outline": 1
    },
    "redhat.java": {
        "completion": 2,
        "outline": 3,
        "codeLens": 4
   }
}

Related issue: #6151

How to test

I've created a sample theia extension https://github.com/JPinkney/Theia-Test-Extension that you clone into theia/packages/ and then add "@theia/test-extension": "^.0.10.0" to the package.json. Then add a plugin to the plugins folder such as vscode-java, vscode-xml. Inside of theia open a java and xml file (so the vscode extensions get activated). Then open up the browsers console and after 10 seconds you should see a printout of the map.

Review checklist

• as an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• as a reviewer, I agree to behave in accordance with the review guidelines

[akosyakov]

it looks good to me, but please see https://github.com/eclipse-theia/theia/pull/6214/files#r326469665

[JPinkney]

@akosyakov I've renamed languages-info to plugin-info as requested. Do you want to take a look again or do you want me to just merge?

[akosyakov]

@JPinkney merge it :)