Support this both for parameters and return types, in all template
functions for calling methods or accessing fields.
To manage the life-time of the temporary objects, create a local stack
frame in the JVM around the calling function. Popping that implicilty
releases all local refernces, so that we don't have to worry about
doing so explicilty. Adding a local reference to the temporary jstring
objects is then enough for the object to live as long as it's needed.
The LocalFrame RAII-like type needs a QJniEnvironment to push and pop
the frame in the JVM, so we don't need a local QJniEnvironment anymore.
Reduce code duplication a bit as a drive-by, and add test coverage.
Change-Id: I801a1b006eea5af02f57d8bb7cca089508dadd1d
Reviewed-by: Tinja Paavoseppä <tinja.paavoseppa@qt.io>
f826d1615a