Enable string arrays in Java methods

[t-arn]

Is your feature request related to a problem? Please describe.
I wanted to call the Android Intent ACTION_OPEN_DOCUMENT where you can pass a String[] with file types.
This creates a rubicon error.
See this PR: beeware/toga#1158

Describe the solution you'd like

1. I would like to be able to pass in String[] to native Java methods (see PR, src/android/toga_android/window.py, open_file_dialog

2. I would like to map String[] to a variable, e.g.
   String = JavaClass("java/lang/String")
   myArray=String("one two three".split(" "))

[t-arn]

Addition: we should also add arrays of classes, e.g. Class.getMethods() returns Method[] which currently creates a rubicon error

[t-arn]

@freakboy3742 Thank you for this rubicon-java addition and for the new release 0.2.6!