main: FieldValue interface

[lavrukov]

No description provided.

[nvamelichev]

@lavrukov Please fix minor checkstyle failures:

Error:  /home/runner/work/yoj-project/yoj-project/databind/src/main/java/tech/ydb/yoj/databind/expression/values/RealFieldValue.java:13:36: 'switch' is not preceded with whitespace. [WhitespaceAround]
Error:  /home/runner/work/yoj-project/yoj-project/databind/src/main/java/tech/ydb/yoj/databind/expression/values/TimestampFieldValue.java:14:36: 'switch' is not preceded with whitespace. [WhitespaceAround]
Error:  /home/runner/work/yoj-project/yoj-project/databind/src/main/java/tech/ydb/yoj/databind/expression/values/NumberFieldValue.java:14:36: 'switch' is not preceded with whitespace. [WhitespaceAround]
Error:  /home/runner/work/yoj-project/yoj-project/databind/src/main/java/tech/ydb/yoj/databind/expression/values/FieldValue.java:37:1: '{' at column 1 should be on the previous line. [LeftCurly]
Error:  /home/runner/work/yoj-project/yoj-project/databind/src/main/java/tech/ydb/yoj/databind/expression/values/StringFieldValue.java:16:36: 'switch' is not preceded with whitespace. [WhitespaceAround]

and this will be ready to merge, I think :-)

[nvamelichev]

TODO: Move FieldValue interface a package up (to where it was) for better compatibility

This is impossible due to rules for sealed classes 😢

[nvamelichev]

UPD: Brought back compatibility FieldValue interface in old package (with deprecation warnings, of course!)

[nvamelichev]

@lavrukov Sasha, please look at this. I've made the FieldValue interface a bit more backwards-compatible then before, for a smooth transition :-)

(And we'll still release this as the next major version, 2.6.0)