[codegen][JAVA] BUG: No regex escaping for Ref fiends

When generating from swagger 2.0 spec @Pattern annotation contains regex which is not escaped if $ref is used for field definition.

Tested for swagger-codegen 2.4.0

Steps to reproduce

Swagger spec:

swagger: '2.0'
info:
  version: '1.0'
  title: Test
paths:
  /command:
    get:
      summary: Test command
      operationId: test
      produces:
        - application/json
      responses:
        200:
          schema:
            $ref: '#/definitions/Root'
definitions:
  Root:
    type: object
    properties:
      memberId:
        $ref: '#/definitions/MemberId'
      anotherId:
        type: string
        pattern: ^\d{10}$
  MemberId:
    type: string
    pattern: ^\d{10}$

Which results in code like this:

@Validated
public class Root   {
  @JsonProperty("memberId")
  private String memberId = null;

  @JsonProperty("anotherId")
  private String anotherId = null;

  public Root memberId(String memberId) {
    this.memberId = memberId;
    return this;
  }

  @ApiModelProperty(value = "")

@Pattern(regexp="^\d{10}$") 
  public String getMemberId() {
    return memberId;
  }

  public void setMemberId(String memberId) {
    this.memberId = memberId;
  }

  public Root anotherId(String anotherId) {
    this.anotherId = anotherId;
    return this;
  }

  @ApiModelProperty(value = "")

@Pattern(regexp="^\\d{10}$") 
  public String getAnotherId() {
    return anotherId;
  }

  public void setAnotherId(String anotherId) {
    this.anotherId = anotherId;
  }
}

We can see @Pattern(regexp="^\d{10}$") for memberId field and @Pattern(regexp="^\\d{10}$") for anotherId. Lack of escaping in memberId produces compilation error due to wrong string literal format.

Related issues/PRs

Validation Contraints of $ref (JSON Reference) components are not generated

Suggest a fix/enhancement

Looks like string escaping is not applied for pattern in $ref fields.

Start by reproducing the issue with the Swagger 2.0 specification and compare the generated Java model's @Pattern annotations for the referenced and inline fields. Trace how the referenced pattern reaches the generated annotation, then verify that both annotations compile with equivalent escaped regex strings.