feat: Language injection for Flow

[jcgueriaud1]

Description

Please list all relevant dependencies in this section and provide summary of the change, motivation and context.

Fixes #287 (issue)

Type of change

• Bugfix
• Feature

Checklist

• I have read the contribution guide: https://vaadin.com/docs/latest/guide/contributing/overview/
• I have added a description following the guideline.
• The issue is created in the corresponding repository and I have referenced it.
• I have added tests to ensure my change is effective and works as intended.
• New and existing tests are passing locally with my change.
• I have performed self-review and corrected misspellings.

Additional for Feature type of change

• Enhancement / new feature was discussed in a corresponding GitHub issue and Acceptance Criteria were created.

It's a first version of the PR since it doesn't cover all the cases.
If the idea is good then we can check with methods can be added.

To create the XML, you can go Settings > Language injections and create your own rule then export it and include it in the XML.

[MarcinVaadin]

Made configuration optional due to https://plugins.jetbrains.com/docs/intellij/language-injection.html#load-the-injection-configuration-in-pluginxml

[github-actions]

Artifact build on last commit: distributions.zip.
For MacOS users: there is a zip inside this zip and Finder unzips them both at once. Use unzip distributions.zip from Terminal or check solution for Archive Manager.