Pattern (regex) always enclosed with '/' (slash)

Description

Hi,

I wanted to implement the pattern (RegularExpression), minLength and maxLength validation attributes on the model generated for aspnetcore, but encountered an issue:
While in most other languages a regex is defined as delimited by a '/', this is not the case in c#.
Instead it is only defined as a string, enclosed by quotes.

Which leaves me with a problem because the slashes are always put around the expression by the addRegularExpressionDelimiter method on DefaultCodegen.java:3915 and there is no easy way to remove them while mustache, I can't generate a proper RegularExpression attribute.

Imho, delimiting the expression with / is something language dependent and should happen nowhere except for in the mustache templates. But I suppose removing them would mean a breaking change for all existing java-like mustache templates using the pattern property. Right?

Do you see an easy way to remove the delimiting characters in case of generating c# code?

Swagger-codegen version

v3.0.23

Swagger declaration file content or url

` public String addRegularExpressionDelimiter(String pattern) {
if (StringUtils.isEmpty(pattern)) {
return pattern;
}

    if (!pattern.matches("^/.*")) {
        return "/" + pattern.replaceAll("/", "\\\\/") + "/";
    }

    return pattern;
}`

Command line used for generation

Steps to reproduce

Generate a project using a custom mustache template for rendering a RegularExpression attribute on a model property:
{{#pattern}} [RegularExpression(@"{{pattern}}")] {{/pattern}}

Related issues/PRs

Suggest a fix/enhancement

Either remove the delimiters or at least remove them in case of c# codegen

Thanks!

Start in DefaultCodegen.java around addRegularExpressionDelimiter at line 3915, then inspect how the custom Mustache template consumes pattern for C# model properties. Reproduce generation with the shown RegularExpression template and define done as producing a valid C# attribute without slash delimiters, while accounting for existing Java-like templates.