OpenJpaDialect passes custom isolation level on to OpenJPA's JDBCFetchPlan configuration

Issue: SPR-12319
Extracted AbstractIdentityColumnMaxValueIncrementer and introduced deleteSpecificValues mode

Issue: SPR-12327
Polishing
Enhance SpEL compilation to cover additional expression types

This change introduces support for compilation of expressions
involving inline lists, string concatenation and method
invocations where the method being invoked is declared
with a varargs parameter. It also fixes a problem with
compiling existing method invocations where the target
method is on a non public type.

Issue: SPR-12328