Dynamic invoke for string concatenation #386

[sergeypospelov]

Description

• Investigated the way of implementing dynamicInvoke bytecode instruction in a common case. In a few words, we need to symbolically analyze bootstrap methods, which is incredibly hard in known cases, since it operates with combinators and includes many native calls.
• Implemented a special case of dynamicInvoke — java.lang.invoke.StringConcatFactory methods.
• Added new tests covering the string concatenation mechanism in Java 11.
• Added a -Xcontext-receivers option to the Kotlin compiler args, which turns on context receivers: https://github.com/Kotlin/KEEP/blob/master/proposals/context-receivers.md
• Refactored: modifier utils for ClassIds, ExecutableIds and FieldIds

Relates to #386

Type of Change

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Automated Testing

New tests: org.utbot.examples.strings.StringConcatTest

Checklist:

• The change followed the style guidelines of the UTBot project
• Self-review of the code is passed
• The change contains enough commentaries, particularly in hard-to-understand areas
• No new warnings
• New tests have been added
• All tests pass locally with my changes

[Damtev]

Code generation changes look good to me