kotlinc requires javac on Windows

[Vladislav0Art]

Describe the bug
Windows' kotlinc calls javac (or java?) in its internals. If there is no javac in PATH the compilation fails. In KotlinTestCompiler we need to search for both kotlinc and javac, and somehow let kotlinc "know" about javac.

To Reproduce
Steps to reproduce the behavior:

1. Run test generation on Windows (ensure no javac is present in PATH; it should be the case it you did not install java manually, from Oracle, for example).
2. Observe compilation errors; see the console output; there should be an error about javac not found.

Expected behavior
Kotlin compilation should work correctly on Windows.

Additional context
Another Windows issue is this one: #407. These two issues are different, yet both relate to Windows compilation.