Multiformat API bug

[ValentinPostindustria]

Describe the bug
When we use the new multiformat API with Native parameters it clears banner and video parameters from the request.

To Reproduce
Steps to reproduce the behavior:

• Run the Demo Kotlin App.
• Run Multiformat example.
• Check request with any proxy.

Expected behavior
The request must contain the banner and video parameters.

[ValentinPostindustria]

During the fixing, we found another bug.
Steps to reproduce:

    private fun createBannerParameters(): BannerParameters {
        val params = BannerParameters()
        params.adSizes = mutableSetOf(org.prebid.mobile.AdSize(300, 250))
        return params
    }

    private fun createVideoParameters(): VideoParameters {
        val params = VideoParameters(listOf("video/mp4"))
        params.adSize = org.prebid.mobile.AdSize(320, 480)
        return params
    }

The request combines these sizes.

          "banner": {
              "format": [
                  {
                      "h": 480,
                      "w": 320
                  },
                  {
                      "h": 250,
                      "w": 300
                  }
              ]
          },
          "video": {
              "h": 250,
              "w": 300
          }

The banner must contain only the second size, the video must contain another size.