[core] fix display of toolbar item icons

[vince-fugnitto]

What it does

Fixes #6513

• fixes the display of toolbar item icons when applications are created
  with a subset of available extensions. The common icons are added to core
  for others to use.

The following limited example application was used during testing:

package.json

{
  "private": true,
  "name": "@theia/example-browser",
  "version": "0.12.0",
  "license": "EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0",
  "theia": {
    "frontend": {
      "config": {
        "applicationName": "Theia Browser Example",
        "preferences": {
          "files.enableTrash": false
        }
      }
    }
  },
  "dependencies": {
    "@theia/console": "^0.12.0",
    "@theia/core": "^0.12.0",
    "@theia/debug": "^0.12.0",
    "@theia/editor": "^0.12.0",
    "@theia/filesystem": "^0.12.0",
    "@theia/getting-started": "^0.12.0",
    "@theia/keymaps": "^0.12.0",
    "@theia/languages": "^0.12.0",
    "@theia/monaco": "^0.12.0",
    "@theia/navigator": "^0.12.0",
    "@theia/outline-view": "^0.12.0",
    "@theia/preferences": "^0.12.0",
    "@theia/terminal": "^0.12.0",
    "@theia/workspace": "^0.12.0"
  },
  "scripts": {
    "prepare": "yarn run clean && yarn build",
    "clean": "theia clean && rimraf errorShots",
    "build": "theiaext compile && theia build --mode development",
    "watch": "concurrently -n compile,bundle \"theiaext watch --preserveWatchOutput\" \"theia build --watch --mode development\"",
    "start": "theia start --plugins=local-dir:../../plugins",
    "start:debug": "yarn start --log-level=debug",
    "test": "wdio wdio.conf.js",
    "test-non-headless": "wdio wdio-non-headless.conf.js",
    "coverage:compile": "yarn build --config coverage-webpack.config.js",
    "coverage:remap": "remap-istanbul -i coverage/coverage.json -o coverage/coverage-final.json --exclude 'frontend/index.js' && rimraf coverage/coverage.json",
    "coverage:report:html": "istanbul report --root coverage --format html",
    "coverage:report:lcov": "istanbul report --root coverage --format lcov",
    "coverage": "yarn coverage:compile && yarn test && yarn coverage:remap && yarn coverage:report:lcov && yarn coverage:report:html"
  },
  "devDependencies": {
    "@theia/cli": "^0.12.0"
  }
}

How to test

• verify that existing toolbar icons are displayed properly

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

Signed-off-by: Vincent Fugnitto [email protected]

[lmcbout]

Looks good
Thanks @vince-fugnitto

[vince-fugnitto]

Looks good
Thanks @vince-fugnitto

Thank you for the review! 😃