BigInteger arithmetic operations with executable-model

[tkobayas]

Support BigInteger arithmetic operators in executable-model.

Currently, a constraint like this fails.

    Person( bigInteger + 7I >= 0 )

[tkobayas]

Hint to proceed:

• Create drools-model-codegen/src/test/java/org/drools/model/codegen/execmodel/bigintegertest/BigIntegerTest by copying BigDecimalTest
• Enhance around RHSPhase.withPossiblyBigDecimalConversion. Create BigIntegerArithmeticExprT by copying BigDecimalArithmeticExprT