Re-use the repeated parts of the resolved field when generating `Comparator`

[yevhenii-nadtochii]

The generated comparator can use several nested fields, which may have a common parent. Ideally, we would like to re-reference these common parts to enhance readability.

Consider the following comparator:

java.util.Comparator.comparing((Traveler traveler) -> traveler.getResidence().getRegion())
        .thenComparing((Traveler traveler) -> traveler.getResidence().getAddress().getIsActual())
        .thenComparing((Traveler traveler) -> traveler.getResidence().getAddress().getCity())
        .thenComparing((Traveler traveler) -> traveler.getResidence().getName().getStructure())
        .thenComparing((Traveler traveler) -> traveler.getResidence().getName());

The following parts are used several times:

1. traveler.getResidence().getAddress() - two invocations.
2. traveler.getResidence().getName() - two invocations.
3. traveler.getResidence() - four invocations.

[alexander-yevsyukov]

It's a nice improvement, but we're at the level of the class, so we cannot extract a variable.

The most ambitious way to address this this:

1. Migrate the compilation to generate Kotlin, instead of Java.
2. Extract all necessary variables in the init { } block.