Support Markdown with Gherkin

[RvRijsselt]

Add support for the .feature.md dialect.

Refer to:
https://github.com/cucumber/gherkin/blob/main/MARKDOWN_WITH_GHERKIN.md

Pros of Markdown with Gherkin:

• Beautiful rendering of the feature files directly in GitHub or any other Markdown reader
• Ability to add links inside and across feature and other markdown files
• Ability to add graphics using Mermaid or any other MD extension
• Ask Mistral
• Ask ChatGPT

[RvRijsselt]

Example:

## Feature: Staying alive

This is about actually staying alive,
not the [Bee Gees song](https://www.youtube.com/watch?v=I_izvAbhExY).

```mermaid
flowchart LR
  User --> A([Eat cucumber])
  User --> B([Blend cucumber])
  B --> C([Drink juice])
```

### Rule: If you don't eat you die

![xkcd|200px](https://imgs.xkcd.com/comics/lunch_2x.png)

`@important` `@essential`
#### Scenario Outline: eating

* Given there are `<start>` cucumbers
* When I eat `<eat>` cucumbers
* Then I should have `<left>` cucumbers

##### Examples:

  | start | eat | left |
  | ----- | --- | ---- |
  |    12 |   5 |    7 |
  |    20 |   5 |   15 |

[Code-Grump]

@gasparnagy Can you comment on whether the markdown flavour is cheeky supported by the C# parser, or if there's a plan to make it so?

[gasparnagy]

As far as I know it is not supported by the C# parser currently. We would need to check how Cucumber solves this and consider to port the solution.

This was a cool initiative from Cucumber couple of years ago, but to be honest I haven't seen that really picked up. But of course if we can easily support it by the parser, why not.

[Code-Grump]

I suspect "easily" is the qualifier here. It doesn't look trivial.

[gasparnagy]

It says that it "only" needs another token matcher: https://github.com/cucumber/gherkin/blob/main/MARKDOWN_WITH_GHERKIN.md#some-notes-about-parsing-mdg

It is implemented currently with TypeScript (https://github.com/cucumber/gherkin/blob/d127e589667568a4a25b7d276e1cffa5b64eb2cd/javascript/src/GherkinInMarkdownTokenMatcher.ts) and Python (https://github.com/cucumber/gherkin/blob/d127e589667568a4a25b7d276e1cffa5b64eb2cd/python/gherkin/token_matcher_markdown.py), so that is what would need to be ported to C#. 200-300 lines of code. The Gherkin project already contains test data and expected results in the same way how it works with Gherkin feature files, so testing should be supported too.