[core] building an application solely with @theia/core does not run

[vince-fugnitto]

Description

If one builds an application only with @theia/core the application does not successfully run.

package.json

{
    "private": true,
    "dependencies": {
        "typescript": "latest",
        "@theia/core": "next"
    },
    "devDependencies": {
        "@theia/cli": "next"
    }
}

Error

contribution-provider.ts:47 TypeError: Cannot read property 'addEventListener' of null
    at b (widget.ts:200)
    at Object.w [as addKeyListener] (widget.ts:219)
    at new e (dialogs.ts:68)
    at Object.t.resolveInstance (instantiation.js:45)
    at resolver.js:72
    at Object.t.resolve (resolver.js:96)
    at container.js:319
    at e._get (container.js:310)
    at e.get (container.js:230)
    at e.dynamicValue (binding_to_syntax.js:69)

Steps to Reproduce:

1. create a folder, and add the package.json from above
2. run yarn
3. run yarn theia build
4. run yarn theia start
5. go to the browser and load the application (localhost:3000)
6. the error is displayed in the console

Additional Info

When adding the extension @theia/getting-started, exceptions regarding the preferences are
thrown and the application fails to load properly (#667)

[vince-fugnitto]

Closing in favor of #7056.