Line continuations for rust step definitions

[kieran-ryan]

🤔 What's changed?

Support line continuation characters for step definition patterns written in rust.

⚡️ What's your motivation?

Fixes cucumber/vscode#116.

🏷️ What kind of change is this?

• :bug: Bug fix (non-breaking change which fixes a defect)

♻️ Anything particular you want feedback on?

What gherkin text will match the below step definition pattern where there are characters on the line after the line continuation? cucumber-rs does not throw any error for this pattern; however, was unable to find a matching gherkin test step.

#[given("a line continuation \
")]
fn hungry_cat(world: &mut AnimalWorld) {
    world.cat.hungry = true;
}

📋 Checklist:

• [x] I agree to respect and uphold the Cucumber Community Code of Conduct
• [x] I've changed the behaviour of the code
  • [x] I have added/updated tests to cover my changes.
• [x] Users should know about my change
  • [x] I have added an entry to the "Unreleased" section of the CHANGELOG, linking to this pull request.

[kieran-ryan]

Behaviour of cucumber-rs from Anything particular you want feedback on? has been validated with great help from @tyranron - thank you - see cucumber-rs/cucumber#319.

A rust step definition pattern containing trailing whitespace cannot match a gherkin test step as the gherkin parser strips trailing whitespace. Modifying cucumber-rs to explicitly inform the user of how to fix such cases is a possibility through a pull request. These cases are thus appropriately accounted for in the unit tests of this pull request.

#[given("a line continuation \
")]
fn hungry_cat(world: &mut AnimalWorld) {
    world.cat.hungry = true;
}