Add support of cucumber expressions

[elchupanebrej]

Cucumber expressions module is a part of the Gherkin toolset. To make pytest-bdd compatible with official tools it has to support cucumber expressions

https://github.com/cucumber/cucumber-expressions#readme
There is the official implementation for python: https://pypi.org/project/cucumber-expressions/

An example implementation can be found here elchupanebrej#76

[jsa34]

This is currently blocked until such time as either named parameters can be returned by Cucumber Expressions, or a suitable solution that adheres to the current syntax expected for pytest-bdd to handle that Cucumber Expressions are positional only at present

[neskk]

@jsa34 I think this should be prioritized.
Cucumber-expressions could work if pytest-bdd does the matching of arguments work by cardinality.
If a parameter name does not match any fixture, it must be coming from the expression.
Using pytest-bdd parsers causes cucumber-language plugins to stop working and won't recognize the step-definitions nor its arguments.
I managed to have a tree-sitter syntax that matches the syntax with "parsers.parse()" but then it fails completely due to confusing the named parameters with parameter types - it looks at {endpoint}, and assumes endpoint is a custom parameter type.

Update: I see that you're working on adding support for named groups in cucumber expressions. I'm not sure it will fix the autocomplete plugin.