Add localization extraction to Theia CLI

[msujew]

What it does

Adds an additional CLI command to the Theia-CLI that allows users to extract their localization keys and default values into a json file. This file can later be used to create translations for Theia using different services (e.g. the default mechanism proposed in #10187).

How to test

1. Create a dummy TypeScript file like this:

import { nls } from '@theia/core/lib/browser/nls';
import { Command } from '@theia/core/lib/common';

const v1 = nls.localize('key1', 'value1');
const v2 = nls.localize('nested/key', 'value2');

const categoryKey = 'category-key';
const command = Command.toLocalizedCommand({
	id: 'id',
	label: 'command-label',
        category: 'category'
}, 'nested/command', categoryKey); // The CLI is able to resolve local references to constants

2. Call the extract command on it using the following CLI call (tune the glob pattern accordingly to your setup):

yarn theia extract -p "**/*.ts" -o out.json

3. Assert that all keys/default values have been correctly extracted from the input file.
4. Try this with different command parameters
5. Create an error by modifying the dummy file:

const test = { key: 'key' }; 
const v1 = nls.localize(test.key, 'value1');

6. Assert that the cli finishes successfully and that any errors are printed into the console along with the source information (file path, line, character)

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

[silvanocerza]

I don't know enough knowledge in Typescript to review the code I think but all in all looks good.

In any case I tested the new command with arduino/arduino-ide and it works great. The json is created as expected and in case of failures the errors are clear and meaningful.

For what it's worth am approving this. 👍
Thanks @msujew! 🙏

[jbicker]

Works exactly as described.

[msujew]

@vince-fugnitto Just to make sure, there's nothing that stops me from merging this PR, right?

[vince-fugnitto]

@vince-fugnitto Just to make sure, there's nothing that stops me from merging this PR, right?

@msujew I'll give it a quick review if that's alright? :)

[msujew]

@vince-fugnitto Please do so :)

[vince-fugnitto]

@msujew I confirmed that:

• the source code changes look good
• the different steps in 'how to reproduce' work well

LGTM! 👍