feat(extensions): Allow seperate release /debug build configuration properties for extensions

[jcassidyav]

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What is the current behavior?

In an extensions.json file you can specify a single set of targetBuildConfigurationProperties which are applied to both debug and release, I want to be able to apply different properties to debug vs release.

What is the new behavior?

Allows you to specify different build properties for debug and release for extensions.

So as not to break existing it adds a new property targetNamedBuildConfigurationProperties where you can specify 'release' or 'debug' properties.

e.g.

 "targetNamedBuildConfigurationProperties": {
        "debug"
            "MTL_ENABLE_DEBUG_INFO" : "INCLUDE_SOURCE",
        },
        "release": {
            "MTL_ENABLE_DEBUG_INFO" : "NO",
        }
    }