output: OutputChannelManager incorrectly imports browser code

[vince-fugnitto]

Bug Description:

The OutputChannelManager incorrectly imports browser code meaning that the backend cannot use the manager:

theia/packages/output/src/common/output-channel.ts

Lines 23 to 24 in 0221c61

	import { MonacoEditorModel } from '@theia/monaco/lib/browser/monaco-editor-model';
	import { MonacoTextModelService, IReference } from '@theia/monaco/lib/browser/monaco-text-model-service';

The OutputChannelManager exists in common (can be used by both the browser and node) and common should not import anything:

• https://github.com/eclipse-theia/theia/wiki/Code-Organization

Steps to Reproduce:

1. attempt to import OutputChannelManager in the backend (node)
2. the application will fail to start with the error:

Failed to start the backend application:
ReferenceError: navigator is not defined
    at /home/evinfug/workspaces/theia/node_modules/@phosphor/domutils/lib/platform.js:18:25
    at Object.<anonymous> (/home/evinfug/workspaces/theia/node_modules/@phosphor/domutils/lib/platform.js:46:3)
    at Module._compile (internal/modules/cjs/loader.js:967:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1004:10)
    at Module.load (internal/modules/cjs/loader.js:815:32)
    at Module._load (internal/modules/cjs/loader.js:727:14)
    at Function.Module._load (electron/js2c/asar.js:769:28)
    at Module.require (internal/modules/cjs/loader.js:852:19)
    at require (internal/modules/cjs/helpers.js:74:18)
    at Object.<anonymous> (/home/evinfug/workspaces/theia/node_modules/@phosphor/domutils/lib/index.js:15:10)

[kittaakos]

Related #4306?

[kittaakos]

The OutputChannelManager incorrectly imports browser

The import is correct; the module is incorrectly in common.