fix: default value with special chars with anyOf

[p-spacek]

What does this PR do?

1. fixes a small specific issue when schema contains default value with special chars next to anyOf.

This schema

       {
          type: 'object',
          properties: {
            car: {
              type: 'object',
              required: ['engine'],
              properties: {
                engine: {
                  anyOf: [
                    {
                      type: 'object',
                    },
                    {
                      type: 'string',
                    },
                  ],
                  default: 'type$1234',
                },
              },
            },
          },

doesn't escape default value

note that an object with anyOf (engine) needs to be inside another object (car), then getInserTextForObject is called with schema { car: {engine: anyOf}}

2. fixes condition to allow null, 0, emptyString, false as a default or const

• the same logic is correctly used in other places

What issues does this PR fix or reference?

no ref

Is it tested? How?

unit-test

[coveralls]

coverage: 84.473% (+0.2%) from 84.313%
when pulling e64b19a on jigx-com:fix/default-value-with-special-chars-with-anyOf
into 86905c1 on redhat-developer:main.

[p-spacek]

fixes condition to allow null,0,emptyString as a default or const
the same logic is correctly used in other places

[p-spacek]

moved outside of the class to be able to use it from global functions

[msivasubramaniaan]

@p-spacek please rebase the repo