nls: rename command that extract localizations

[paul-marechal]

Rename the @theia/cli command to extract localizations from sources to
something that would make it explicit enough. extract alone is a bit
too generic.

Change --pattern/-p into an array of --files/-f.

Minor changes.

How to test

Same as #10247

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 nls-extract --files "**/*.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

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[paul-marechal]

@msujew I forgot to submit the small review I made for your PR that adds the localization extractor :S

Here are some suggested changes (just few renames really) that I think would be better. Since those are not published yet I figured now is the time to nitpick.

Tell me what you think :)

[msujew]

LGTM! The names fit better and everything continues to work as expected 👍