feat: update error message for reserved self function argument

[Gusarich]

Issue

Closes #1735.

Checklist

• I have updated CHANGELOG.md
• I have added tests to demonstrate the contribution is correctly implemented: this usually includes both positive and negative tests, showing the happy path(s) and featuring intentionally broken cases
• I have run all the tests locally and no test failure was reported
• I have run the linter, formatter and spellchecker
• I did not do unrelated and/or undiscussed refactorings

[anton-trunov]

I think this will produce a confusing error message

extends fun foo(self: Int, self: String) { }

Parameter name "self" is reserved for functions with "extends" modifier

Here it is an extends function, it's just we have duplicate parameter names

[anton-trunov]

Suggested change

	if (params.length > 0) {
	const [firstParam, ...restParams] = params;
	const [head, ...restParams] = params;
	if (!isUndefined(head)) { // from ../utils/array