Unifies naming for isMap in Schema class properties

[spacether]

We are using multiple properties that mean this schema is type object. The properties are:

• isMapContainer
• isMapModel

This PR updates our java classes that implement Schema to be consistent in out naming and getters and setters for this property. These classes have been updated:

• CodegenProperty
• CodegenModel
• CodegenParameter
• CodegenResponse

Note: this is a map version of this array PR
This PR

• changes isMapContainer + isMapModel to isMap.
• is a feature break out for [REQ] Implement needed common isX properties in java Schema classes in openapi core #7651

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Core Team Members
@wing328 (2015/07) ❤️
@jimschubert (2016/05) ❤️
@cbornet (2016/05)
@ackintosh (2018/02) ❤️
@jmini (2018/04) ❤️
@etherealjoy (2019/06)
@spacether (2020/05)

[wing328]

Overall it looks good but I didn't check every single files.

There's only 1 file change in the sample and that change looks good to me.