Add '.d.ts' DTO generator

[evidolob]

What does this PR do?

Provide new DTO generator for TypeScript which can generate .d.ts file
To enable new generator add:

<dts>true</dts>

in <configuration> section of che-core-typescript-dto-maven-plugin

What issues does this PR fix or reference?

#12132

Also this pull use string union literals for Java Enum types:

export interface MyCustom  {
   status?: 'SHUTDOWN' | 'ALIVE';
}

and adds super interfaces to DTO type declaration:

  // org.eclipse.che.plugin.typescript.dto.MySuperClassDTO
  export interface MySuperClass  {
    name?: string;
  } 
  // org.eclipse.che.plugin.typescript.dto.MyOtherDTO
  export interface MyOther extends MySuperClass {
    name?: string;
  } 

[benoitf]

Hello @evidolob awesome

I don't see new integration tests there to validate the dto files like there ?
it is not part of this PR ?https://github.com/eclipse/che/blob/5cefbf63442b6b36a74d5180aa1a0b64f576dcd0/core/che-core-typescript-dto-maven-plugin/src/it/java/org/eclipse/che/plugin/typescript/dto/TypeScriptDTOGeneratorMojoITest.java