[BUG][Java][Spring]`allowUnicodeIdentifiers` to false does not sanitize parameter names

Description

When allowUnicodeIdentifiers is set to true, the parameters name are not sanitize in the spring generated source code.

openapi-generator version

The openapi-generator version is the current master.

OpenAPI declaration file content or url

openapi: 3.0.1
info:
  description: Sanitize for tags
  version: 1.0.0
  title: Sanitize for tags
paths:
  '/sanitize-tags':
    get:
      summary: Check the class when generated with useTags option
      tags:
      - créances
      parameters:
        - name: créance
          in: path
          required: true
          schema:
            type: string
      responses:      
        200:
          $ref: '#/components/responses/201'
components:
  responses:
    200:
      description: Get

Command line used for generation

Command line:

java -jar ~/git/github/openapi-generator/modules/openapi-generator-cli/target/openapi-generator-cli.jar generate -g spring -i tag.openapi.yaml -c java-config.json -o ./tags

And the configuration file

{
    "library": "spring-boot", 
    "groupId": "a.group.id", 
    "artifactId": "an-artifact-id",
    "artifactVersion": "0.1.0-SNAPSHOT", 
    "sourceFolder": "src/main/java", 
    "configPackage": "my.api.config", 
    "modelPackage": "my.api.model", 
    "apiPackage": "my.api.resource",
    "dateLibrary": "java8",
    "useBeanValidation": true, 
    "interfaceOnly": true, 
    "implicitHeaders": true, 
    "swaggerDocketConfig": true, 
    "useTags": true, 
    "allowUnicodeIdentifiers": false
}

Steps to reproduce

I tried allowUnicodeIdentifiers this weekend. I set it to true with the following openapi file.
It works as expected for interface. The parameter name use é character in the name.

default ResponseEntity<Void> sanitizeTagsGet(@ApiParam(value = "",required=true) @PathVariable("créance") String créance) {

When I set allowUnicodeIdentifiers to false, the result is the same. As I understand the parameter name should be sanitize.

default ResponseEntity<Void> sanitizeTagsGet(@ApiParam(value = "",required=true) @PathVariable("créance") String créance) {

For french language, it will be great to have the following result :

default ResponseEntity<Void> sanitizeTagsGet(@ApiParam(value = "",required=true) @PathVariable("créance") String creance) {

Related issues/PRs

Don't find any

Suggest a fix

I'm not sure if the problem comes from sanitize methods or in mustache templates.

Use the supplied OpenAPI YAML and Spring generation command as the reproduction case. Inspect the Spring generator's parameter-name sanitization path and the Mustache templates, then compare output with allowUnicodeIdentifiers set to true and false. Done means the false setting produces the sanitized parameter identifier creance while preserving the original path-variable mapping.