Description

The problem is that we add utbot_tests as kotlin-test root (see .iml file for module, the line looks like
<sourceFolder url="file://$MODULE_DIR$/utbot_tests" type="kotlin-test" /> in case we add it initially for .kt source file. It's not a problem when it doesn't break a workflow. But it did.

1. Show all test roots (Java and Kotlin) in combobox, the choice is up to user.
2. Generation support for Kotlin is not stable, thus codegen language was renamed toKotlin (experimental) for a while.

Fixes#497

Type of Change

Please delete options that are not relevant.

• Minor bug fix (non-breaking small changes)

How Has This Been Tested?

Manual Scenario

See steps and attached project in the issue

Checklist (remove irrelevant options):

• The change followed the style guidelines of the UTBot project
• Self-review of the code is passed
• No new warnings