feat: add new rule no-duplicate-keyframe-selectors

[snitin315]

Prerequisites checklist

• I have read the contributing guidelines.

What is the purpose of this pull request?

Add new rule no-duplicate-keyframe-selectors.

What changes did you make? (Give an overview)

Examples of incorrect code for this rule:

/* eslint css/no-duplicate-keyframe-selectors: "error" */

@keyframes test {
	0% {
		opacity: 0;
	}

	0% {
		opacity: 1;
	}
}

@keyframes test {
	from {
		opacity: 0;
	}

	from {
		opacity: 1;
	}
}

@keyframes test {
	from {
		opacity: 0;
	}

	from {
		opacity: 1;
	}
}

Examples of correct code for this rule:

/* eslint css/no-duplicate-keyframe-selectors: "error" */

@keyframes test {
	0% {
		opacity: 0;
	}

	100% {
		opacity: 1;
	}
}

@keyframes test {
	from {
		opacity: 0;
	}

	to {
		opacity: 1;
	}
}

Related Issues

Fix #141

Is there anything you'd like reviewers to focus on?

[snitin315]

Added this test.css for local testing purposes, similar to the eslint repo

[snitin315]

I'm not sure why TS reports error here, it seems to be valid. AST

[Tanujkanti4441]

We need to add conditions here to check the types

Suggested change

	// @ts-ignore - prelude is a valid property
	const selector = child.prelude.children[0].children[0];
	// @ts-ignore - prelude is a valid property
	const selector = child.type === "Rule" && child.prelude.type === "SelectorList" && child.prelude.children[0].type === "Selector" && child.prelude.children[0].children[0];