Allow to use operator tokens as functions

[ckganesan]

This PR enables the usage of operator tokens as functions. #572

[antonmedv]

Lets just allow to use "endsWith"
"startsWith"
"contains"
"matches" words as method names?

[ckganesan]

Lets just allow to use "endsWith" "startsWith" "contains" "matches" words as method names?

I have made the necessary updates based on your feedback.

[Q16G]

This function is very important for my code, could you please add this function to the latest version with a tag, so that I can add it to the code

[antonmedv]

Let's try to implement this feature without adding additional options. I will try to do it.

[ckganesan]

Let's try to implement this feature without adding additional options. I will try to do it.

I have removed option functionality from configuration as per your feedback

[antonmedv]

Awesome work!

[antonmedv]

I actually not understand what original issues is was about: #568

Is to be able to use reuse operator names as functions:

	options := []expr.Option{
		expr.Function(
			"contains",
			func(params ...any) (any, error) {
				return false, nil
			},
			new(func() bool),
		),
	}

	program, err := expr.Compile(`contains()`, options...)

I think this is a bad practice and not should be allowed. Also I think it's bad decision to allow to use some operators as functions =/

Let's not processed this this PR @ckganesan?

[Q16G]

operator becomes a function to increase the extensibility, convenient for users to customize or extend. Consider a scenario where the user needs to pass in multiple arguments to the contains function, and the original operator is not satisfied, we can extend it to contain from an operator to a function

[antonmedv]

Consider a scenario where the user needs to pass in multiple arguments to the contains function

Can you show some examples?

[Q16G]

Because I think this allows the user to customize a higher degree, the experience will be better

[Q16G]

Will this operation be allowed

[antonmedv]

No. For now, not. I don't see a use case. And adding such feature complicates parser and type checker.