[cpp-qt5] Escape language reserved symbols which are valid in the spec

[etherealjoy]

Description

When the specification contains valid symbols which are language specific operators compilation fails.

openapi-generator version

3.0.0

OpenAPI declaration file content or url

This is a valid snippet from a spec

  v1.HostPathType:
    type: object
    additionalProperties:
      type: string

Creates the following snippet of code for Qt5 for example

class OAIV1.HostPathType: public OAIObject {

This code will not compile for any C++ client and server.
I would suppose the same issue for other langs like C#

Suggest a fix/enhancement

The '.' and other valid symbols for example has to be escaped for example to '_' to make compilation pass.

[etherealjoy]

Following code in DefaultCodegen.java is not working for this case

public String sanitizeName(String name, String removeCharRegEx)
...
        // input.name => input_name
        name = name.replaceAll("\\.", "_");

[etherealjoy]

Solved in #388