Replace the generic Step function with Given/When/Then functions to match the majority of other languages

### 🤔 What's the problem you're trying to solve?

I'm trying to add support for Go (godog) to Cucumber language service, so that we can finally use Go BDD support in VSCode.

It's a bit tricky because of the generic `Step` func and not having the separate `Given/When/Then` funcs instead.

Raised a poll here: https://github.com/cucumber/godog/discussions/542

### ✨ What's your proposed solution?

- Mark the `Step` function as deprecated
- Add 3 new functions to match their respective counterparts in the feature files - `Given/When/Then`

### ⛏ Have you considered any alternatives or workarounds?

No alternatives considered. I think we should "just" do this to keep the syntax consistent with other programming languages.

### 📚 Any additional context?

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The issue names no files or tests; start by locating the existing generic Step function and its callers, then review the linked godog discussion for the API expectations. Done means Step is deprecated and separate Given, When, and Then functions are available with syntax matching the feature-file counterparts.

Written by the indexing model from the issue text.