feat: Add possibility to choose theme in android dialogs

[ReazerDev]

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• Tests for the changes are included - https://github.com/NativeScript/NativeScript/blob/master/tools/notes/WritingUnitTests.md.

What is the current behavior?

Right now, you can't change the theme for android dialogs.

What is the new behavior?

A theme attribute has been added to change the theme of android dialogs. Available themes are: https://developer.android.com/reference/android/R.style