Escaped $ref values result in funky names

Description

Referenced schemas that have percent-encodings in their pointer are serialized inconsistently.

Swagger-codegen version

Whatever is on generator.swagger.io and generator3.swagger.io 😄

Swagger declaration file content or url

Swagger 2.0:

swagger: "2.0"
info:
  title: Escaped $ref bug
  description: Generate a server or client to see the problem
  version: "1.0"
paths:
  /:
    get:
      responses:
        200:
          description: ok
          schema:
            $ref: '#/definitions/My%21Strange%21Name%21'
definitions:
  My!Strange!Name!:
    type: string

OpenAPI 3.0:

openapi: "3.0.0"
info:
  title: Escaped $ref bug
  description: Generate a server or client to see the problem
  version: "1.0"
paths:
  /:
    get:
      responses:
        200:
          description: ok
          content:
            application/json:
              schema:
                $ref: '#/definitions/My%21Strange%21Name%21'
definitions:
  My!Strange!Name!:
    type: string

Command line used for generation

n/a

Steps to reproduce

Generate a client from the definition (I used JavaScript, but others will reproduce this as well).

For Swagger 2: observe that MyStrangeName and My21Strange21Name21 are used inconsistently, which results in a broken client.

For OpenAPI 3: observe a 500 Internal Server Error.

Related issues/PRs

Previously discussed in https://github.com/swagger-api/swagger-editor/issues/1766.

Suggest a fix/enhancement

Percent-encodings should be consistently stripped from generated names.